FOUNDATIONS 


OF 


BRIDGES   AND    BUILDINGS 


BY 


HENRY  S.  J^COBY 

PROFESSOR   OF  BRIDGE  ENGINEERING,   CORNELL   UNIVERSITY 


AND 


ROLAND  P.  DAVIS 

PROFESSOR  OF  STRUCTURAL  AND  HYDRAULIC   ENGINEERING 
WEST  VIRGINIA  UNIVERSITY 


FIRST  EDITION 


MCGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1914 


s 


COPYRIGHT,  1914,  BY  THE 
McGR/w-HiLL  BOOK  COMPANY,  INC. 


THE. MAPLE. PRE8Q. YOUR. PA 


PREFACE 

In  preparing  this  volume  the  aim  of  the  authors  has  been  to 
treat  in  a  systematic  manner  the  entire  subject  of  foundations 
for  bridges  and  buildings  as  represented  by  American  engineer- 
ing practice.  Only  occasional  references  are  made  to  foreign 
practice.  It  was  hoped,  at  first,  to  accomplish  this  task  within 
the  limits  of  about  300  pages,  but  as  the  work  progressed  it 
became  evident  that  this  could  not  be  done  without  abbreviat- 
ing the  treatment  of  many  topics  so  much  as  to  become  un- 
satisfactory. In  many  cases,  space  has  been  economized  by 
inserting  additional  illustrations  and  reducing  descriptions  in 
the  text. 

A  large  proportion  of  space  is  devoted  to  piles  and  pile  driving, 
since  young  engineers  are  more  likely  to  obtain  their  early 
experience  with  pile  foundations  than  with  any  other  class  of 
foundation  construction.  Many  facts  derived  from  experience 
are  given  to  emphasize  and  illustrate  the  application  of  funda- 
mental principles  and  to  form  a  rational  basis  for  that  kind 
of  judgment  which  is  such  an  important  element  in  an  engineer's 
professional  practice.  The  undesirable  features  of  considerable 
pile  driving  in  this  country  have  been  due  as  much  to  the  as- 
sumption that  the  art  of  pile  driving  is  so  simple  that  the  aid  of 
science  is  not  essential,  as  to  the  attempt  of  some  engineers  to 
base  the  art  upon  theoretical  rules  which  fail  to  take  into 
account  many  practical  factors  of  the  problem.  Another 
reason  for  extending  the  treatment  is  due  to  the  recent  intro- 
duction of  concrete  piles  which  will  help  to  retain  the  dominant 
place  that  pile  foundations  have  held  heretofore  among  other 
classes  of  foundations. 

The  attention  of  engineering  teachers  is  called  to  the  arrange- 
ment of  the  topics  in  the  first  five  chapters.  Instead  of  combin- 
ing the  treatment  of  all  kinds  of  piles  in  chapters  on  descriptions, 

v 


VI  PREFACE 

equipment,  driving,  and  bearing  power  respectively,  the  subject 
is  developed  in  accordance  with  pedagogical  principles  for  the 
benefit  of  students  who  approach  it  without  any  previous 
knowledge  of  the  subject.  It  is  believed,  however,  that 
practicians  will  find  this  arrangement  equally  useful  for  their 
study  and  reference.  The  full  discussion  of  the  bearing 
power  of  timber  piles  before  considering  that  of  concrete  piles, 
conforms  also  to  the  order  of  historical  development. 

The  treatment  of  the  pneumatic  process  and  its  application, 
to  both  bridges  and  buildings,  is  supplemented  by  a  chapter  on 
pneumatic  caisson  practice  by  T.  KENNARD  THOMSON,  an 
experienced  consulting  engineer  who  has  specialized  in  founda- 
tion construction.  The  results  of  his  experience  and  ob- 
servation should  be  helpful  to  all  engineers  and  contractors 
of  lesser  experience. ' 

Three  chapters  on  piers  and  abutments  are  incorporated  in 
this  work  since  courses  of  instruction  in  technical  colleges 
frequently  include  these  topics  in  masonry  construction  with 
foundations.  During  the  past  decade  considerable  improve- 
ments have  been  made  in  the  design  of  piers  and  abutments 
by  the  introduction  of  new  types,  including  hollow  and  arched 
forms,  in  order  to  reduce  the  loads  upon  foundation  beds  and  to 
eliminate  a  large  part  of  the  lateral  thrust  of  embankments, 
as  well  as  to  decrease  the  volume  of  masonry  in  some  cases. 

The  limits  of  the  volume  precluded  historical  notes  in  con- 
nection with  every  class  of  foundation,  but  they  are  introduced 
in  certain  cases  relating  to  new  types  of  construction,  or  where 
the  process  of  development  indicates  the  features  which  are 
likely  to  persist  in  the  future. 

Since  a  subject  embracing  so  many  details  of  design  and 
construction  cannot  be  exhaustively  treated  in  a  single  volume 
of  convenient  size  to  meet  the  needs  of  all  practicians,  a  chapter 
has  been  added  which  contains  a  large  number  of  carefully 
selected  and  classified  references  to  the  vast  amount  of  illus- 
trative material  on  foundations  contained  in  engineering 
periodicals  and  the  proceedings  of  engineering  societies.  It  is 
hoped  that  young  technical  graduates  will  form  the  habit  of 


PREFACE  Vll 

consulting  the  article?  referred  to,  making  suitable  abstracts, 
and  filing  them  for  future  use.  To  compare  the  manner  in 
which  different  designers  have  solved  a  given  problem  is  a 
most  valuable  study. 

Grateful  acknowledgments  for  photographs  are  due  to  S.  W. 
BOWEN,  A.  S.  CRANE,  A.  0.  CUNNINGHAM,  Dravo  Contracting 
Co.,  Lackawanna  Steel  Co.,  RALPH  MODJESKI,  C.  K.  MOHLER, 
J.  H.  PRIOR,  J.  R.  RABLIN,  E.  J.  SCHNEIDER,  H.  E.  STEVENS, 
F.  L.  THOMPSON,  and  M.  M.  UPSON;  to  J.  Q.  BARLOW,  J.  D. 
ISAACS,  and  H.  K.  SELTZER  for  permission  to  reproduce  draw- 
ings; to  R.  A.  CUMMINGS,  Engineering  News,  Engineering 
Record,  Engineering  and  Contracting,  and  Railway  Age 
Gazette  for  permission  to  reprint  illustrations;  to  C.  W. 
REINHARDT  for  the  excellent  drawings  from  which  a  number 
of  illustrations  were  reproduced;  and  to  E.  H.  CONNOR,  L.  L. 
DAVIS,  WALTER  FERRIS,  J.  E.  GREINER,  H.  IBSEN,  A.  R. 
RAYMER,  R.  TRIMBLE,  and  many  other  engineers  who  have 
kindly  furnished  information.  Acknowledgment  is  made  for 
several  photographs  on  the  half-tones  themselves,  or  their 
titles. 

April  15,  1914. 


CONTENTS 

PREFACE PAGE      v 

LIST  OF  FULL-PAGE    ILLUSTRATIONS xv 

CHAPTER  I 
TIMBER  PILES  AND  DRIVERS 

ART.    i.  Foundations PAGE        i 

2.  Classification  of  Piles 2 

3.  Timber  Piles 6 

4.  Form  and  Dimensions 9 

5.  The  Phenomena  of  Pile  Driving n 

6.  Ordinary  Pile-drivers 14 

7.  Track  Pile-drivers 16 

8.  The  Drop  Pile-hammer 20 

9.  The  Steam  Pile-hammer 21 

10.  Advantages  of  Steam-hammers 24 

11.  Rings,  Caps,  and  Followers 27 

12.  Points,  Shoes,  and  Splices 32 

CHAPTER  II 
DRIVING  TIMBER  PILES 

ART.  13.  Observations  in  Practice PAGE      37 

14.  Driving  Piles  Butt  Down 40 

15.  Driving  Batter  Piles 41 

16.  Use  of  the  Water-jet 43 

17.  Equipment  for  Water-jet  Process 48 

18.  Overdriving  Piles 49 

19.  Spacing  of  Piles 55 

20.  Cutting  off  and  Removing  Piles 58 

21.  Chemical  Preservation 63 

22.  Mechanical  Protection 66 

23.  Cost  of  Pile  Driving 71 

CHAPTER  III 
BEARING  POWER  OF  PILES 

ART.    24.  Piles  Acting  as  Columns PAGE      75 

25.  The  Goodrich  Formula 77 

26.  Engineering  News  Formula 82 

ix 


X  CONTENTS 

ART.    27.  Weight  and  Fall  of  Hammer PAGE      85 

28.  The  Restrained  Fall 87 

29.  Final  Penetration  per  Blow 88 

30.  Formula  for  Steam-hammer 90 

31.  Tables  and  Diagrams 92 

32.  Effect  of  Rest  on  Bearing  Power 95 

33.  Effect  of  Sub-surface  Conditions 97 

34.  On  Total  Penetration 100 

35.  Degree  of  Security 101 

36.  Test  Piles 105 

37.  Pile  Records  and  Performance no 

38.  Specifications 112 


CHAPTER  IV 
CONCRETE  PILES 

ART.    39.  Introduction  and  Classification PAGE    116 

40.  Relative  Advantages 118 

41.  Unpatented  Pre- molded  Piles 122 

42.  Patented  Pre- molded  Piles 127 

43.  Form  and  Construction 130 

44.  Design  of  Pre-molded  Piles 134 

45.  Cast-in-place  Piles 136 

46.  Precautions  Against  Injury 142 

47.  Composite  Types  and  Combination  Piles .  144 

48.  Drivers,  Hammers,  and  Caps 147 

49.  Driving  Concrete  Piles 152 

50.  Analysis  of  Time  and  Cost 157 

51.  Formulas  for  Bearing  Power 161 

52.  Choice  of  Type 163 

53.  Effect  of  Taper 166 

54.  Driving  and  Loading  Test  Piles 169 

55.  Specifications 172 


CHAPTER  V 
METAL  AND  SHEET  PILES 

ART.    56.  Tubular  Piles PAGE    174 

57.  Disk  and  Screw  Piles 178 

58.  Sand  Piles 180 

59.  Timber  Sheet-piling 181 

60.  Steel  Sheet-piling 184 

61.  Concrete  Sheet-piling 189 

62.  Driving  Sheet-piling 190 

63.  Design  of  Sheet-piling 194 


CONTENTS  XI 

CHAPTER  VI 

COFFERDAMS 

ART.    64.  The  Cofferdam  Process PAGE    198 

65.  Earth  Cofferdams 199 

66.  Wooden  Sheet-pile  Cofferdams 203 

67.  Single  Wall  with  Guide  Piles 206 

68.  Sheet-piling  Supported  by  Frames 210 

69.  Sheet-piling  Supported  by  Cribs .' 214 

70.  Steel  Sheet-pile  Cofferdams 216 

71.  Self-supporting  Steel  Sheet-pile  Cofferdams 221 

72.  Crib  Cofferdams 226 

73.  Movable  Cofferdams 228 

74.  Miscellaneous  Types. 232 

75.  Puddle  and  Leakage 234 

76.  Design  of  Cofferdams 235 

77.  Cost  of  Cofferdams 236 

78.  Choice  of  Type 238 


CHAPTER  VII 
BOX  AND  OPEN  CAISSONS 

ART.    79.  Definitions  and  Classification PAGE    239 

80.  Box  Caissons  of  Timber 240 

81.  Box  Caissons  of  Concrete 243 

82.  Miscellaneous  Types 245 

83.  Single- wall  Open  Caissons 246 

84.  Cylinder  Caissons 251 

85.  Metal  Cylinder  Caissons 254 

86.  Reinfo reed-concrete  Cylinder  Caissons 257 

87.  Open  Caissons  with  Dredging  Wells 262 

88.  Construction  with  Timber 263 

89.  Construction  with  Metal 270 

90.  Construction  with  Concrete 272 

91.  Sinking  Open  Caissons '  277 


CHAPTER  VIII 
PNEUMATIC  CAISSONS  FOR  BRIDGES 

ART.    92.  The  Pneumatic  Process PAGE    280 

93.  Caisson  Roof  Construction 283 

94.  Sides  of  Working  Chamber 293 

95.  Details  of  Cutting  Edge 294 

96.  Bracing  of  Caisson 296 

97.  Crib  Construction 298 

98.  Cofferdam  Construction 300 


Xll  CONTENTS 

ART.    99.  Pneumatic  Caissons  of  Concrete PAGE  301 

100.  Pneumatic  Caissons  of  Metal 302 

101.  Cylinder  Pier  Caissons 304 

102.  Combination  Cylinder  Caissons 307 


CHAPTER  IX 
PNEUMATIC  CAISSONS  FOR  BRIDGES 

ART.  103.  Shafts  and  Air-locks PAGE   309 

104.  Design  of  Caissons 313 

105.  Building  and  Placing  the  Caisson 315 

106.  Sinking  the  Caisson 317 

107.  Removing  Spoil  from  Working  Chamber 319 

108.  Concreting  the  Air  Chamber ,'. ",;- 322 

109.  Rate  of  Sinking 3  23 

no.  Frictional  Resistance 326 

in.  Physiological  Effects  of  Compressed  Air 329 

112.  Prevention  of  Caisson  Disease 333 


CHAPTER  X 
PNEUMATIC  CAISSONS  FOR  BUILDINGS 

ART.  113.  General  Development PAGE    338 

114.  Caissons  of  Timber 340 

115.  Caissons  with  Metal  Shells 345 

1 1 6.  Caissons  of  Wood  and  Steel 347 

117.  Caissons  of  Reinforced  Concrete 349 

118.  Crib  and  Cofferdam 350 

119.  Shafts  and  Air-locks 352 

120.  Sinking  the  Caisson 356 

121.  Rate  of  Sinking 359 

122.  Filling  the  Air  Chamber 360 

123.  Water-tight  Dam  of  Wall  Piers 361 


CHAPTER  XI 
PIER  FOUNDATIONS  IN  OPEN  WELLS 

ART.  124.  Open  Wells  with  Sheet-piling PAGE   366 

125.  Open  Wells  with  Sheeting;  the  Chicago  Method    ....  370 

126.  The  Grouting  Process 373 

127.  Applications  and  Tests 376 

128.  The  Freezing  Process 379 

129.  Hydraulic  Caissons 382 


CONTENTS  Xlll 

CHAPTER  XII 
ORDINARY  BRIDGE  PIERS 

ART.  130.  General  Requirements PAGE    384 

131.  Definitions 386 

132.  Form  and  Dimensions 388 

133.  Materials  and  Construction 394 

134.  Examples  of  Solid  Piers 398 

135.  Examples  of  Hollow  Piers « 403 

136.  Stability  of  Piers 409 

137.  Example  of  Pier  Design .        .  411 

CHAPTER  XIII 
CYLINDER  AND  PIVOT  PIERS 

ART.  138.  General  Arrangement PAGE    417 

139.  Metal-shell  Cylinder  Piers ...  418 

140.  Design  and  Construction 423 

141.  Reinforced-concrete  Cylinder  Piers 426 

142.  Large  Cylinder  or  Pivot  Piers 428 

CHAPTER  XIV 
BRIDGE  ABUTMENTS 

ART.  143.  Form  and  Dimensions PAGE    433 

144.  Design  and  Construction 436 

145.  Wing-wall  Abutments 439 

146.  U-abutments  and  T-abutments 441 

147.  Buried  Abutments 447 

148.  Reinforced  Arch  Abutments 449 

/       CHAPTER  XV 
\/  SPREAD  FOUNDATIONS 

ART.  149.  General  Considerations PAGE  452 

150.  Early  Types  of  Footings 453 

151.  Modern  Types  of  Spread  Foundations 457 

152.  Construction  of  I-Beam  Grillages 458 

153.  Design  of  I-beam  Grillages 459 

154.  Design  of  Double-column  Footings .  464 

155.  Distribution  of  Pressure  on  Base 468 

156.  Steel  Grillage  Foundations 469 

157.  Design  of  Reinforced-concrete  Spread  Foundations.  .    .    .  474 

158.  Design  of  Reinforced-concrete  Column  Footings    ....  477 

159.  Concrete  Spread  Foundations 481 


XIV  CONTENTS 

CHAPTER  XVI 
UNDERPINNING  BUILDINGS 

ART.  1 60.  Needle-beam  Underpinning PAGE    490 

161.  Examples  with  Needle-beams 493 

162.  Supporting  Wall  below  Beams 495 

163.  The  Cantilever  Method 497 

164.  Figure-four  Needles 501 

165.  Placing  the  New  Foundation 503 

166.  Joining  to  the  Old  Wall 506 

167.  The  Breuchaud  Process 507 

168.  Method  of  Sinking  Cylinders 511 

169.  Concreting  the  Cylinders 513 

170.  Transferring  Load  to  Cylinder 514 

171.  Other  Modern  Methods 515 


v      CHAPTER  XVII 

EXPLORATIONS  AND  UNIT  LOADS 

>/ 
ART.  172.  Test  Pits  and  Sounding  Rods PAGE    518 

173.  Borings  with  Augers , 5T9 

174.  Wash  Borings 520 

175.  Core  Drillings  with  Diamonds 524 

176.  Core  Drilling  without  Diamonds 527 

177.  Need  of  Sub-surface  Explorations 529 

178.  Tests  for  Bearing  Capacity 531 

179.  Values  of  Bearing  Capacity , 534 


CHAPTER  XVIII 
PNEUMATIC  CAISSON  PRACTICE 

ART.  180.  Historical  Notes PAGE    538 

181.  Results  of  Evolution 539 

182.  Construction  of  Caissons ,  54* 

183.  Caulking,  Shafts  and  Lighting 544 

184.  Methods  of  Launching 547 

185.  Placing  and  Sinking 549 

186.  Excavating  and  Sealing 552 

187.  Joints  between  Caissons 554 

188.  Plant  and  Equipment 555 

189.  Air-locks  and  Concrete 556 

190.  Allowable  Bearing  under  Caissons 559 

191.  Remarks  on  Underpinning 560 


CONTENTS  XV 

CHAPTER  XIX 
REFERENCES  TO  ENGINEERING  LITERATURE 

ART.  192.  Literature  on  Foundations PAGE    562 

193.  Timber  Piles  and  Pile  Driving 567 

194.  Bearing  Power  of  Piles 572 

195.  Concrete  Piles 573 

196.  Metal  and  Sheet  Piles 575 

197.  Cofferdams 577 

198.  Box  and  Open  Caissons 580 

199.  Pneumatic  Caissons  for  Bridges 582 

200.  Pneumatic  Caissons  for  Buildings 585 

201.  Pier  Foundations  in  Open  Wells 587 

202.  Bridge  Piers 588 

203.  Bridge  Abutments 591 

204.  Spread  Foundations 592 

205.  Underpinning  Buildings 593 

206.  Explorations  and  Unit  Loads .  595 

INDEX. PAGE    599 

LIST  OF  FULL-PAGE  ILLUSTRATIONS 


A  Standard  Type  of  Contractor's  Pile-driver PAGE      15 

Self-propelling  Track  Pile-driver Xi6 

Self-propelling  and  Convertible  Crane  Pile-drivers 1i7 

Locomotive  Crane  Used  as  Traveler  and  Pile-driver 18 

Driving  Batter  Piles  for  Trestle  at  Dumbarton  Point X42 

Examples  of  Overdriven  Piles  Exposed  by  Excavation J43 

Steel  Pile-driver  and  Sections  of  Reinforced  Steel  Shells ^36 

Sections  of  Patented  Steel  Sheet-piling   . 186 

Driving  Wakefield  Sheet-piling  for  a  Cofferdam *I9O 

Cofferdams  with  Single  Walls  of  Timber  Sheet-piling 207 

Self-supporting  Timber  Sheet-pile  Cofferdam ^14 

Timber  Bracing  of  Steel  Sheet-pile  Cofferdam 122o 

Self-supporting  Steel  Sheet-pile  Cofferdam :222 

Bulging  Walls  of  Steel  Sheet-pile  Cofferdam ^23 

Box  Caisson  for  Pivot  Pier  of  Highway  Bridge 241 

Open  Caisson  for  Pivot  Pier  of  Railroad  Bridge 256 

Reinforced-concrete  Cylinder  Caisson  and  Forms 260 

Open  Caisson  of  Timber  with  Two  Dredging  Wells 265 

Open  Caisson  of  Timber  with  Six  Dredging  Wells 267 

Open  Caisson  of  Concrete  with  Four  Dredging  Wells 273 

Open  Caisson  of  Concrete  with  Three  Dredging  Wells ^76 

1  Half-tone  illustration  facing  the  page  indicated. 


XVI  ILLUSTRATIONS 

Forms  for,  and  Cracks  in,  Open  Caissons  of  Concrete PAGE  '277 

Pneumatic  Caisson  for  Pier  of  Bellefontaine  Bridge 285 

Pneumatic  Caisson  for  Pier  of  New  Quebec  Bridge 286 

Pneumatic  Caisson  for  Pier  of  Municipal  Bridge 290 

Pneumatic  Caisson  for  Cylinder  Pier 305 

Material  Lock  for  Pneumatic  Caisson,  Memphis  Bridge  ......  310 

Caissons  on  Launching  Ways  and  Supported  by  Barges ^id 

Launching  a  Caisson  from  a  Pontoon X3 1 7 

Pneumatic  Foundation  with  Wells  below  Caisson 325 

Sinking  Caissons  for  the  Municipal  Building ^46 

Sinking  Open  Wells  for  Column  Piers  of  Kinney  Building ^70 

Open  Well  with  Sectional  Lining  for  Bridge  Pier I3?i 

Pier  of  Gray's  Ferry  Bridge,  Philadelphia,  Pa ^oo 

Pier  of  Cantilever  Bridge  at  Thebes,  Illinois 14oi 

Pier  of  McKinley  Bridge  at  St.  Louis,  Missouri *402 

Pier  of  Victoria  Bridge  near  Montreal,  Ontario .  ^03 

Pier  of  O.-W.,  R.  &  N.  Co.  at  Portland,  Oregon 408 

Cylinder  Piers  of  C.  &  N.  W.  Ry.  Bridge  at  Clinton,  Iowa     ....  J4i6 

Cylinder  Piers  of  Avon  River  Bridge,  Windsor,  N.  S »  422 

Railroad  Bridge  with  U-abutments  at  Melrose,  Mass ^36 

U-abutment  with  Unequal  Bearing  on  Foundation X437 

Diagram  of  Forces  Acting  on  an  Abutment 438 

Abutments  of  Bridge  over  Colvin  St.,  Buffalo,  N.  Y :440 

Abutments  of  Railroad  Bridge  near  Mandan,  N.  D J44i 

Reinforced-concrete  Abutment,  Wabash  R.  R.,  Monticello,  111.  .    .    .    ^40,  ^41 

Typical  Plain  Concrete  U-abutment,  C.  M.  &  St.  P.  Ry 442 

Bridge  Abutment  with  Reinforced-concrete  Deck 444 

T-abutments  of  Single-track  Railroad  Bridge !446 

Concrete  Arch  Abutments  of  C.  M.  &  St.  P.  Ry.  Bridge :45o 

Reinforced-concrete  Arch  Abutment  of  Lind  Viaduct *45 1 

Column  Footings  of  Plate  Girders  and  I-beam  Grillages 473 

Reinforced-concrete  Spread  Foundation  with  Arch  Inverts 487 

Arrangement  of  Underpinning,  92  Maiden  Lane,  New  York   ....  499 

Underpinning  with  Figure-four  Needle  Method 502 

Use  of  Long  Shores  for  Cross  Building,  New  York *502 

Details  of  Cylinder  for  Underpinning  Stokes  Building 510 

1  Half-tone  illustration  facing  the  page  indicated. 


FOUNDATIONS    OF 
BRIDGES   AND    BUILDINGS 

CHAPTER  I 
TIMBER  PILES  AND  DRIVERS 

ART.  i.     FOUNDATIONS 

A  structure  usually  consists  of  two  parts  one  of  which  is  sup- 
ported by  the  other;  the  upper  part  being  known  as  the  super- 
structure and  the  lower  part  as  the  substructure.  •  In  a  bridge 
the  superstructure  is  composed  of  the  beams,  girders,  or  trusses, 
together  with  the  floor  system  and  bracing  which  they  carry; 
while  the  substructure  consists  of  the  piers  and  abutments, 
including  their  supporting  bases. 

.  The  substructure  frequently  consists  of  two  parts  which  differ 
more  or  less  in  form  and  character,  the  lower  part  being  called 
the  foundation  which  supports  the  rest  of  the  entire  structure. 
Sometimes  the  term  foundation  is  used  without  regard  to  any 
substructure;  as,  for  example,  when  it  is  applied  to  the  independ- 
ent structure  which  supports  a  machine. 

The  foundation  of  a  structure  may  then  be  defined  as  that 
part  of  it  which  is  usually  placed  below  the  surface  of  the  ground 
and  which  distributes  the  load  upon  the  earth  beneath. 

Foundations  are  divided  into  various  classes.  The  simplest 
form  is  obtained  by  widening  merely  the  base  of  a  wall  or  pier,  so 
as  to  distribute  the  load  over  a  sufficient  area  on  the  foundation 
bed  of  earth.  Another  form  is  known  as  the  spread  footing,  in 
which  the  bearing  area  is  enlarged,  either  by  reinforcing  the 
concrete  base  with  steel  bars  or  by  inserting  one  or  more  tiers  of 
steel  beams. 

I 


2  TIMBER   PILES   AND   DRIVERS  CHAP.  I 

Pile  foundations  consist  of  a  base  of  concrete  or  of  timber 
grillage,  supported  by  piles  which  distribute  the  load  to  the  earth 
through  a  considerable  depth,  either  by  friction  alone  or  by 
friction  combined  with  bearing  on  the  ends  of  the  piles. 

When  the  bottom  of  the  foundation  has  to  be  located  on 
a  bed  of  hard  material  at  a  considerable  depth  below  the  surface 
of  the  ground,  the  classes  of  foundations  are  distinguished  by 
the  respective  methods  required  to  sink  them  into  position. 

Foundations  built  in  open  wells  are  used  when  the  excavation 
can  be  made  either  in  the  dry  or  with  no  more  interference  by 
water  than  may  be  controlled  by  a  reasonable  amount  of 
pumping. 

When  open  caissons  are  employed,  the  excavation  is  made 
through  the  water  under  ordinary  atmospheric  conditions,  and 
after  the  bottom  is  sealed  by  concrete  the  rest  of  the  foundation 
is  built  in  the  open  air. 

Pneumatic  foundations  are  those  in  which  the  excavation  is 
made  by  working  in  compressed  air  in  the  chamber  of  a  caisson, 
on  the  roof  of  which  the  concrete  or  masonry  is  built  up  in  the 
open  air  during  the  operation  of  sinking. 

Many  kinds  of  foundations  also  require  the  use  of  a  temporary 
structure  known  as  a  cofferdam  in  order  to  exclude  the  water 
from  the  site  of  the  foundation  during  its  construction. 

The  character  of  the  earth  at  the  site,  extending  down  to  the 
bed  on  which  it  is  to  be  founded,  and  the  influence  of  water,  if 
any,  determine  the  kind  of  foundation  to  be  employed  in  any 
given  case;  with  due  regard,  however,  to  economic  limitations. 

These  general  classes  of  foundations  and  their  subdivisions 
will  be  described  and  illustrated  in  the  subsequent  chapters  of 
this  volume,  together  with  the  general  methods  of  placing  them 
in  position.  Occasional  notes  on  some  of  the  special  equipment 
required  will  also  be  given. 

ART.  2.     CLASSIFICATION  or  PILES 

A  pile  is  an  element  of  construction  placed  in  the  ground,  either 
vertically  or  nearly  so,  to  increase  its  power  to  sustain  the  weight 
of  a  structure,  or  to  resist  a  lateral  force. 


ART.  2  CLASSIFICATION   OF   PILES  3 

Piles  are  designated  by  the  material  of  which  they  are  com- 
posed; as,  for  example,  timber  piles;  by  their  form  of  cross-sec- 
tion, as  round  or  octagonal  piles;  by  their  inclination,  as  batter 
piles;  by  their  use,  as  guide  piles,  sheet  piles  or  fender  piles; 
or  by  some  attachment  to  their  feet  in  order  to  increase  their 
bearing  power,  as  screw  piles  or  disk  piles. 

A  bearing  pile  is  one  which  carries  a  superimposed  load.  Its 
form  of  cross-section  depends  upon  the  material  of  which  it  is 
composed,  and  may  be  round  or  circular,  square,  hexagonal  or 
annular.  Its  longitudinal  section  is  frequently  tapering,  but 
sometimes  its  cross-section  remains  uniform  throughout  the 
length  of  the  pile. 

The  head  of  a  pile  is  its  upper  end;  the  foot  of  a  pile  is  its 
lower  end;  the  butt  of  a  pile  is  its  larger  end;  the  tip  of  a 
pile  is  its  smaller  end.  These  definitions  show  that  the  terms 
head  and  foot  relate  to  the  pile  in  its  final  position  only,  while 
the  terms  butt  and  tip  apply  to  a  tapered  pile  either  before  or 
after  it  is  placed  in  position. 

The  term  '  top'  is  often  applied  to  one  end  of  a  pile  but  this  is 
ambiguous,  since  the  upper  end  of  the  pile  in  the  tree  may  be 
either  the  upper  or  the  lower  end  after  the  pile  is  driven;  its 
use  should  therefore  be  discouraged.  The  same  objection  holds 
with  respect  to  the  term  '  point,'  which  is  often  used  to  desig- 
nate the  small  end  of  the  pile,  which  may  be  either  point- 
ed or  left  blunt  by  cutting  off  the  end  perpendicular  to  the 
axis  of  the  pile. 

A  batter  pile  is  one  driven  at  an  inclination  to  resist  forces 
which  are  not  vertical.  They  are  sometimes  called  spur  piles. 
When  a  pile  structure  is  built  to  resist  lateral  pressure,  expe- 
rience has  proven  the  importance  of  relying  chiefly  upon  batter 
piles,  rather  than  upon  the  cross-bracing  of  vertical  piles,  to 
insure  lateral  stability.  When  piles  are  employed  to  resist  the 
lateral  pressure  of  earth  and  to  form  a  wall  which  is  intended  to 
be  water-tight,  they  are  called  sheet  piles.  Their  form  usually 
differs  from  that  of  other  piles,  there  being  a  considerable  va- 
riety in  their  cross-sections  both  for  timber  as  well  as  steel  sheet 
piles.  The  subject  of  sheet-piling  is  discussed  in  Chap.  V  and 


4  TIMBER   PILES   AND  DRIVERS  CHAP.  I 

various  applications  are  given  in  subsequent  chapters.  Short 
piles  are  sometimes  driven  in  order  to  compress  and  consolidate 
the  ground  over  a  considerable  area  to  increase  its  bearing 
power,  but  usually  this  result  is  more  economically  attained  by 
means  of  sand  piles,  perhaps  combined  with  sand  or  cinder  filling 
on  top. 

Bearing  piles  are  used  in  foundation  construction  under  two 
typical  conditions:  first,  when  the  piles  are  driven  through  soft 
or  fluid  material  into  or  to  a  stratum  of  firm  or  practically 
unyielding  material;  second,  when  no  hard  bottom  can  be 
reached  by  any  reasonable  length  of  pile  and  the  friction  of  the 
pile  in  the  ground  is  sufficient  to  support  the  load  with  safety. 

In  the  first  case,  the  pile  receives  little  if  any  lateral  support 
and  therefore  acts  as  a  column;  while  in  the  second  case,  the 
true  pile  action  occurs  and  the  load  is  either  limited  by  the  adhe- 
sion of  the  ground  to  the  surface  of  the  pile  or  the  compressive 
resistance  of  the  material  in  the  upper  part  of  the  pile. 

Bearing  piles  located  in  streams  often  have  to  resist  lateral 
forces  due  to  the  impact  of  drift,  ice,  etc.  As  far  as  possible  such 
forces  should  be  provided  for  by  sway  or  lateral  bracing. 

The  most  favorable  condition  for  the  use  of  bearing  piles 
occurs  when  a  firm  stratum  can  be  reached  by  piles  of  ordinary 
dimensions,  and  therefore  easily  obtainable  in  the  markets,  and 
the  overlying  material  is  compressible,  so  as  to  be  readily  pene- 
trated by  piles,  but  sufficiently  compact  to  prevent  the  piles 
from  bending  and  lateral  displacement. 

Guide  piles  are  used  to  support  the  horizontal  timbers  or 
wales  which  in  turn  guide  and  support  the  vertical  sheet-piling. 
Their  principle  application  occurs  in  cofferdam  construction 
(see  Art.  67),  but  they  are  also  used  in  ferry  slips,  and  to  aid 
in  locating  and  sinking  open  and  pneumatic  caissons  in  streams 
or  lakes. 

Fender  piles,  as  their  name  implies,  are  driven  at  wharfs  or  in 
front  of  large  masonry  structures  or  other  important  works, 
to  protect  them  from  sudden  blows  by  vessels.  In  addition  to 
the  uses  of  piles  mentioned  above,  they  are  employed  in  dikes, 
jetties,  and  other  structures. 


AST.  2  CLASSIFICATION   OF   PILES  5 

Timber  piles  are  very  extensively  employed  in  railroad  con- 
struction and  maintenance;  for  trestle  bridges,  either  as  tem- 
porary structures  until  the  filling  in  of  embankments  or  more 
permanent  bridges  of  steel  or  concrete  can  be  built  to  replace 
them,  or  until  they  are  reconstructed  of  the  same  material. 
Trestle  bridges  with  pile  foundations  are  generally  built  in 
emergencies  resulting  from  washouts,  fire,  or  accidents  of  any 
kind.  This  is  due  to  the  rapidity  with  which  the  pile  foundation 
can  be  put  in  place  and  the  rest  of  the  structure  built;  piles  and 
large  dimension  timbers  for  framing  being  regularly  carried  in 
stock.  Guide  piles,  fender  piles,  and  in  fact  all  piles  used  in 
temporary  structures  are  likewise  composed  of  wood. 

It  will  hence  be  noted  that  piles  are  very  extensively  used 
in  modern  engineering  construction.  While  it  is  certain  that 
timber  piles  were  known  as  long  ago  as  the  early  lake  dwellers  of 
Europe,  they  have  been  used  continuously  since  that  time,  for 
foundation  purposes.  On  the  contrary,  concrete  piles  were 
introduced  in  the  opening  years  of  the  twentieth  century. 
Metal  piles  were  first  used  in  1838. 

The  materials  employed  for  piles  include  wood,  concrete 
(either  plain  or  reinforced),  cast  iron,  wrought  iron,  steel  and 
sand.  Sometimes  two  materials  are  used  in  combination;  as. 
for  example,  in  a  wooden  pile  surrounded  by  a  protection  of 
reinforced  concrete,  or  in  a  hollow  metal  pile  filled  with  concrete, 
either  with  or  without  reinforcement.  Piles  composed  of  sand 
are  made  in  place  in  the  earth  in  a  vertical  cavity  formed  for 
the  purpose  and  hence  serve  chiefly  to  compact  the  earth  and 
thereby  increase  its  bearing  power. 

In  practice,  a  pile  is  usually  placed  in  position  in  the  ground  by 
driving  it  with  a  steam-hammer  or  a  drop-hammer,  either  with 
or  without  the  aid  of  one  or  more  water -jets.  In  rare  instances, 
a  pile  may  be  sunk  in  place  by  static  pressure,  either  by  means  of 
block  and  tackle  or  a  weight  of  some  kind.  Sand  piles  or  certain 
types  of  concrete  piles  are,  however,  cast  directly  in  place. 

The  principal  use  of  piles  occurs  in  the  foundations  of  bridges, 
buildings  and  other  structures  in  which  they  act  simply  as 
bearing  piles. 


^  6  TIMBER   PILES   AND   DRIVERS  CHAP.  I 


ART.  3.     TIMBER  PILES 

In  the  specifications  for  timber  piles  adopted  in  1909  by  the 
American  Railway  Engineering  Association,  the  following  kinds 
of  wood  are  included  for  piles  intended  for  standard  construction 
purposes  and  designated  as  'railroad  heart  grade':  white,  burr, 
and  post  oak;  longleaf  pine;  Douglas  fir;  tamarack;  eastern 
white  and  red  cedar;  chestnut;  western  cedar;  redwood  and 
cypress.  For  temporary  construction,  the  following  kinds  of 
wood  are  included  for  piles  designated  as  'railroad  falsework 
grade':  red  and  all  other  oaks,  not  included  in  railroad  heart 
grade;  sycamore;  sweet,  black  and  tupelo  gum;  maple;  elm; 
hickory;  Norway  pine  or  any  sound  timber  that  will  stand 
driving. 

The  principal  difference  between  these  two  grades  relates  to 
durability,  although  the  former  includes  several  of  the  most 
valuable  species  of  wood  used  in  modern  engineering  construc- 
tion, as  longleaf  yellow  pine,  Douglas  fir  and  white  oak.  Cedar 
piles  are  noted  for  their  long  life  or  durability.  Spruce  is  not 
specifically  mentioned  in  these  specifications,  although  spruce 
piles  are  extensively  used,  especially  in  New  England,  both  for 
railroad  structures  and  other  buildings.  Spruce  from  certain 
localities  has  unusual  toughness,  giving  the  piles  increased  resist- 
ance to  the  tendency  to  split  and  broom  when  driven. 

Among  other  species  which  have  been  used  to  a  very  limited 
extent  for  piles  may  be  mentioned  beech,  ash  and  basswood. 
In  Florida,  palmetto  piles  are  used,  as  this  wood  is  comparatively 
free  from  attacks  of  marine  borers,  known  as  the  teredo.  White 
pine  piles  were  used  in  the  northern  central  states  before  the 
close  of  the  nineteenth  century,  but  since  then  this  species  has 
become  too  valuable  on  account  of  its  demand  for  other  uses  in 
building  construction.  Yellow  pine,  Douglas  fir,  spruce,  cedar 
and  other  conifers  have  increased  value  for  piles  because  they 
are  so  straight  and  free  from  large  branches,  and  can  be  obtained 
in  greater  lengths.  The  longest  piles  used  in  single  sticks  are 
Douglas  fir.  Oak  piles  are  hard  and  tough,  but  are  not  so 
straight  and  smooth  and  have  the  added  disadvantages  on 


ART.  3  TIMBER   PILES  7 

account  of  weight,  of  increased  cost  of  transportation,  and  of 
liability  to  sink  in  water  unless  lighter  logs  are  used  in  rafts  to 
buoy  them  up. 

The  specifications  of  the  American  Railway  Engineering 
Association  also  include  the  following  requirements,  for  the 
railroad  heart  grade:  Piles  shall  be  cut  from  sound  trees;  shall 
be  close  grained  and  solid,  free  from  defects,  such  as  injurious 
ring  shakes,  large  and  unsound  or  loose  knots,  decay  or  other 
defects,  which  may  materially  impair' their  strength  or  durabil- 
ity. Piles  must  be  cut  above  the  ground  swell  and  have  a  uni- 
form taper  from  butt  to  tip.  Short  bends  will  not  be  allowed. 
A  line  drawn  from  the  center  of  the  butt  to  the  center  of  the  tip 
shall  lie  within  the  body  of  the  pile.  Unless  otherwise  allowed, 
piles  must  be  cut  when  the  sap  is  down.  Piles  must  be  peeled 
soon  after  cutting.  All  knots  shall  be  trimmed  close  to  the  body 
of  the  pile.  Square  piles  shall  show  at  least  80  percent  heart 
on  each  side  at  any  cross-section  of  the  stick,  and  all  round  piles 
shall  show  at  least  loj  inches  diameter  of  heart  at  the  butt. 
Piles  of  the  railroad  falsework  grade,  however,  need  not  be 
peeled,  and  no  limits  are  specified  as  to  the  diameter  or  propor- 
tion of  heart.  These  specifications  as  revised,  from  time  to 
time,  are  published  in  the  Manual  of  the  American  Railway 
Engineering  Association. 

The  provision  regarding  the  lateral  curvature  of  a  pile  is  modi- 
fied by  some  engineers  so  that  the  center  of  any  cross-section 
shall  not  depart  more  than  one-eighth  of  its  diameter  from  the 
straight  line  joining  the  centers  of  the  butt  and  tip.  In  another 
specification,  this  distance  is  made  i  percent  of  the  length  of 
the  pile.  When  a  pile  has  bends  in  two  directions,  it  is  regarded 
as  a  sufficient  cause  for  rejection  on  first-class  work.  It  has  been 
found  by  experience  that  spruce  piles  selected  for  their  straight- 
ness  and  smoothness  could  be  driven  satisfactorily  where  it 
was  impossible  to  drive  oak  piles,  which  were  irregular  in  shape 
and  covered  with  knots.  Timber  piles  are  driven  with  the 
butt  down  under  some  conditions,  this  topic  being  discussed 
in  Art.  14. 

The  time  of  year  in  which  timber  is  cut  for  piles  does  not 


8  TIMBER  PILES   AND  DRIVERS  CHAP.  I 

receive  the  degree  of  attention  which  it  deserves.  It  affects 
both  the  strength  of  the  timber  and  its  durability.  Tests  made 
in  Germany  on  four  spruce  trees,  growing  close  together  in  the 
same  soil,  showed  that  if  the  strength,  when  cut  in  December,  is 
taken  as  100  percent,  those  cut  in  January,  February,  and  March 
had  strengths  of  88,  80,  and  62  percent  respectively.  "Beech 
timber  cut  in  December  and  January  gave  an  average  mechan- 
ical life  of  six  years,  whereas  the  same  kind  of  timber  cut  in  the 
same  location  in  February  and  March  gave  a  service  of  only 
two  years." 

Experience  in  this  country  has  also  shown  conclusively,  that 
the  use  of  piles  of  the  best  species  of  wood  may  lead  to  serious 
loss  when  it  is  cut  in  the  summer  and  left  only  a  short  time 
before  the  bark  is  peeled.  Decay  due  to  fungi  and  the  ravages 
of  worms,  which  became  manifest  when  the  sapwood  began  to 
decay,  required  in  one  case  involving  a  very  large  number  of 
piles,  the  replacement  of  the  whole  lot  within  four  years,  some 
of  them  being  eaten  through  entirely  within  two  years  (see  Rail- 
road Gazette,  vol.  31,  page  865,  Dec.  15,  1899). 

Foundation  piles  when  cut  off  below  the  ground-water  level, 
apparently  have  an  indefinite  life.  For  example,  in  recon- 
structing a  bridge,  timber  piles  were  removed  which  indicated 
no  material  decay  after  being  in  service  600  years.  A  still  more 
conspicuous  example  was  brought  to  the  attention  of  engineers 
and  architects,  when  the  Campanile  of  St.  Mark's  in  Venice 
fell  in  1902.  The  piles  in  the  foundation  which  had  been  in 
service  for  1002  years  were  found  to  be  in  such  a  good  state  of 
preservation  that  they  were  allowed  to  remain  to  support  the 
reconstructed  tower. 

A  lagged  pile  has  pieces  of  timber  bolted  around  the  sides  of 
the  pile,  in  order  to  increase  its  bearing  power.  It  increases 
the  area  of  cross-section  and  also  the  surface  of  the  sides  of  the 
pile  which  is  of  more  importance,  since  such  piles  are  used  only 
in  very  soft  material.  The  New  York  City  Dock  Department 
made  a  test  in  1902  of  the  relative  bearing  power  of  lagged  and 
unlagged  piles  driven  in  North  River  mud,  the  results  of  which 
are  recorded  in  Trans.  Am.  Soc.  C.  E.  (1905),  vol.  54  F,  pages  8 


ART.  4  FORM  AND   DIMENSIONS  9 

and  27.  The  discussion  by  the  author  of  the  paper  implies 
that  the  ultimate  bearing  power  was  increased  about  50  percent. 
The  total  penetration  of  the  piles  ranged  from  47.1  to  52.6 
feet,  while  the  lagging  was  only  30  feet  in  length.  Although  it  is 
not  stated  what  position  vertically  the  lagging  occupied,  it 
appears  that  the  surface  in  contact  with  the  mud  was  increased 
about  70  percent.  An  expert  on  pile  driving  has  expressed  the 
opinion  that  the  lagging  of  piles  is  unnecessary  and  relatively 
costly.  In  general  practice,  lagged  piles  are  rarely  ever  used, 
and  it  may  therefore  be  concluded  that  they  are  not  desirable. 

ART.  4.     FORM  AND  DIMENSIONS 

Since  a  timber  pile  generally  consists  of  the  lower  portion  of 
the  trunk  of  a  tree,  after  its  branches  and  bark  are  removed, 
.and  the  knots  trimmed  close  to  the  body,  its  cross-section  is 
round  or  approximately  circular.  Square  piles  are  rarely 
used  as  bearing  piles,  and  only  to  a  limited  extent  for  special 
purposes,  one  of  which  is  to  form  large  timber  sheet  piles  by  the 
addition  of  scantlings  on  two  sides  to  form  tongue-and-groove 
joints.  Since  the  introduction  of  steel  sheet-piling,  there  is  but 
little  need  for  framing  sheet  piles  out  of  1 2  by  1 2-inch,  or  even 
larger,  timbers  (see  Art.  59). 

The  specifications  referred  to  at  the  beginning  of  the  preced- 
ing article  contain  the  following  paragraph,  relating  to  dimen- 
sions: For  round  piles,  the  minimum  diameter  at  the  tip  shall 
be  9  inches,  for  lengths  not  exceeding  30  feet;  8  inches  for  lengths 
over  30  feet  but  not  exceeding  50  feet;  and  7  inches  for  lengths 
over  50  feet.  The  minimum  diameter  at  one-quarter  of  the 
length  from  the  butt  shall  be  12  inches,  and  the  maximum  diam- 
eter at  the  butt  20  inches.  The  same  requirements  apply  to 
the  square  pile,  by  substituting  thickness  for  diameter. 

The  relation  between  the  diameters  of  butt  and  tip  depends 
upon  the  length  of  a  pile  and  naturally  varies  for  different  spe- 
cies of  wood.  The  diameters  of  piles  for  ordinary  buildings  are 
usually  somewhat  smaller  than  for  bridges  and  very  heavy 
buildings,  but  the  diameter  of  tip  should  not  be  less  than  6  inches 


10  TIMBER   PILES    AND   DRIVERS  CHAP.  I 

in  any  case.  When  a  pile  acts  principally  as  a  column,  it  should 
have  a  larger  tip  than  if  its  resistance  depends  mainly  on  friction. 

The  clearance  between  the  leads  of  pile  drivers,  and  between 
which  piles  must  be  placed  to  drive  them,  is  ordinarily  2  2  inches 
and  it  will  be  noted  that  the  maximum  limit  placed  upon  the 
diameter  of  butt,  in  the  specifications  quoted  above,  is  2  inches 
less.  It  may  be  stated  that  the  diameter  of  butt  usually  ranges 
from  ii  to  1 6  inches  in  foundations  which  are  neither  intended 
for  very  light  not  exceptionally  heavy  structures. 

The  length  of  a  pile  necessarily  depends  upon  the  character 
of  the  earth  into  which  it  is  to  be  driven.  Piles  as  short 
as  10  feet  have  been  used  but  it  is  questionable  whether  this  is 
not  too  low  a  minimum.  In  ordinary  construction,  the  length 
of  piles  varies  roughly  from  20  to  40  feet.  As  an  illustration  of 
the  use  of  long  piles,  Douglas  fir  piles  ranging  in  length  from  60 
to  120  feet  were  driven  in  1907  for  the  trestle  approaches  of  the 
Dumbarton  bridge  at  San  Francisco  Bay,  the  penetrations  in 
some  cases  being  as  great  as  60  feet.  The  tip  was  not  less  than 
9  inches,  while  the  butt  was  limited  to  22  inches.  In  the  jetty 
construction  at  the  mouth  of  the  Columbia  River  piles  130  feet 
long  were  driven  50  feet  into  the  bed  of  the  river;  they  were  30 
inches  in  diameter  at  the  butt.  Even  greater  lengths  up  to  175 
feet  were  formerly  used  on  the  Pacific  Coast,  but  since  the  best 
timber  next  to  the  coast  or  navigable  streams  has  been  cut,  the 
available  lengths  are  limited  by  the  conditions  of  railroad  trans- 
portation. Where  the  character  of  the  earth  or  of  the  several 
strata  to  be  penetrated  is  fairly  uniform  over  the  area  of  a 
given  site,  it  is  desirable  to  use  piles  as  nearly  alike  in  diameter 
and  length  as  can  be  secured  economically  in  the  available 
markets.  Where  the  driving  is  easy  a  small  pile  is  frequently  as 
advantageous  as  a  large  one;  but  where  the  driving  is  hard  a 
large  pile  is  required  so  as  to  have  the  necessary  strength  and 
stiffness  to  stand  the  driving. 

The  principles  of  good  design  and  economic  construction 
require  the  proper  lengths  of  piles  to  be  determined  in  advance. 
In  the  absence  of  definite  knowledge  by  previous  pile-driving 
experience  at  the  same  location  or  contiguous  to  it,  a  careful 


ART.  5  THE   PHENOMENA   OF   PILE   DRIVING  1 1 

exploration  of  the  ground  should  be  made  by  means  of  auger  or 
wash-borings  or  by  means  of  test  piles.  Tests  should  be  made  at 
certain  intervals  along  the  line  of  a  trestle  bridge,  at  the  loca- 
tions of  piers  and  abutments,  or  at  several  places  distributed 
over  the  area  of  a  building  foundation.  Driving  test  piles  is 
advantageous,  since  it  furnishes  information  at  the  same  time  on 
the  number  of  blows  required  to  secure  the  necessary  total  pene- 
tration and  hence,  the  approximate  time  for  the  subsequent 
work.  This  item  alone  is  frequently  worth  far  more  than  the 
cost  of  the  investigation.  On  the  other  hand,  emergencies  may 
arise  in  which  the  value  of  such  preliminary  tests  in  saving 
material  and  labor  in  construction  may  be  offset  by  a  greater 
loss  due  to  delay  in  resuming  traffic  operations.  Methods 
of  making  explorations  by  different  appliances  are  described 
in  Chap.  XVII. 

If  some  other  method  is  used  to  determine  the  supporting 
power  of  the  earth,  and  it  is  proposed  to  compute  the  size  of 
pile,  it  is  well  to  consider  that "  with  the  usual  methods  in  vogue, 
in  which  large  initial  stresses  are  to  be  expected,  it  is  not  safe  to 
use  piles  of  diameters  which  would  be  just  large  enough  to  sup- 
port the  developed  supporting  power  of  the  earth,  nor  would  it 
be  practicable  to  secure  or  drive  them." 

A  convenient  table  prepared  by  E.  O.  FAULKNER,  for  cal- 
culating the  volume  of  piling  in  cubic  feet,  and  which  is  based  on 
the  prismoidal  formula,  may  be  found  in  Eng.  News,  vol.  54, 
page  170,  or  in  RICKEY'S  Building  Foreman's  Pocket-book. 

ART.  5.     THE  PHENOMENA  OF  PILE  DRIVING 

The  term  pile  driving  is  applied  to  the  operation  of  taking  a 
pile  and  forcing  it  into  a  definite  position  in  the  ground  without 
previous  excavation.  A  number  of  different  methods  are 
employed  for  this  purpose  which  require  different  kinds  of  equip- 
ment. Historically  the  oldest  method  of  driving  a  pile  is  by 
means  of  a  hammer.  While  very  small  bearing  piles,  or  posts, 
were  doubtless  driven  at  first  by  hand  with  a  maul  or  beetle, 
those  of  larger  size  usually  designated  as  piles  required  the  use  of 


12  TIMBER   PILES   AND  DRIVERS  CHAP.  I 

a  machine  by  which  a  hammer  was  raised  with  the  aid  of  a  pulley 
and  rope  and  allowed  to  drop  on  the  head  of  the  pile.  A  weight 
used  in  this  manner  was  hence  called  a  drop-hammer.  At  first 
men,  then  horses,  and  afterward  the  steam  engine  were  used  to 
raise  the  hammer. 

After  the  invention  of  the  steam  engine,  steam-hammers  were 
designed  in  which  the  driving  weight  is  lifted  a  short  distance 
by  steam  pressure  and  allowed  to  fall  by  gravity,  the  rapidity  of 
action  being  greatly  increased.  Subsequently  steam-hammers 
were  invented  in  which  steam  pressure  reinforces  the  action  of 
gravity  on  the  down  stroke.  At  one  time  pressure  due  to  the 
explosion  of  gunpowder  was  used  to  drive  piles  but  that  method 
is  now  regarded  as  antiquated.  To  a  very  limited  extent  pile 
driving  has  been  accomplished  by  placing  a  static  weight  upon 
a  pile  and  rocking  it  to  and  fro  in  soft  ground,  to  which  condi- 
tion this  method  is  practically  limited. 

Another  method  of  more  recent  discovery  which  has  greatly 
advanced  the  art  of  pile  driving  consists  in  the  use  of  the  water- 
jet  to  aid  in  displacing  the  earth  at  the  foot  of  the  pile  and  to 
lessen  the  friction  of  the  pile  as  it  descends  through  the  surround- 
ing material.  This  method  is  generally  employed  in  conjunc- 
tion with  the  use  of  a  hammer,  although  occasionally  the  hammer 
may  serve  merely  as  a  Static  weight  during  a  portion  of  the  time 
required  to  sink  the  pile. 

The  phenomena  of  pile  driving  may  perhaps  be  most  readily 
understood  by  the  student  by  considering  the  case  in  which  a 
timber  pile  is  driven  vertically  into  the  ground  by  means  of  a 
drop-hammer.  After  the  piles  are  delivered  on  the  site  within 
reach  of  one  of  the  lines  of  the  pile-driver  which  is  used  to 
handle  the  piles,  the  line  is  made  fast  to  a  pile  near  its  head 
and  first  dragged,  if  necessary,  close  to  the  front  of  the  pile- 
driver,  and  then  hoisted  until  it  is  suspended  in  the  air.  It  is 
next  placed  and  held  laterally  between  the  pair  of  tall  parallel 
members  of  the  pile-driver  known  as  the  leads  and  between 
which  the  hammer  is  guided  in  its  movements.  After  lowering 
the  pile  until  its  foot  rests  on  the  ground,  the  line  is  released. 
The  hammer,  being  held  at  the  top  of  the  leads  by  the  other 


ART.  5  THE   PHENOMENA   OF   PILE   DRIVING  13 

line,  is  now  released  and  in  falling  strikes  the  head  of  the 
pile.  It  is  then  raised  again  and  released  for  the  second  blow, 
and  so  on  for  successive  blows  until  the  required  penetration 
of  the  pile  is  obtained. 

During  its  fall  the  velocity  of  the  hammer  is  accelerated  until 
the  instant  when  the  hammer  and  the  pile,  in  connection  with 
a  certain  mass  of  earth  beneath  and  around  it,  move  together. 
When  the  hammer  strikes  the  head  of  the  pile  the  pressure 
between  the  pile  and  hammer  increases  from  zero  up  to  a  certain 
value  when  the  pile  as  a  whole  begins  to  move.  After  all  the 
compression  in  both  hammer  and  pile  has  taken  place  they  will 
move  together.  Their  velocity  is  then  gradually  reduced  to  zero 
by  the  varying  resistance  of  the  earth  during  the  time  of  pene- 
tration for  the  pile.  Some  of  the  work  done  by  the  falling  ham- 
mer is  consumed  in  overcoming  friction,  in  crushing  and  heating 
the  head  of  the  pile,  and  in  compressing  the  pile  and  hammer, 
while  the  remainder  causes  the  penetration  of  the  pile. 

In  careful  experimental  investigations  conducted  by  ERNEST 
P.  GOODRICH,  with  an  apparatus  designed  to  show  the  exact 
vertical  motion  of  the  pile,  the  time  occupied  by  this  motion, 
the  velocity  of  the  hammer  as  it  strikes  the  pile,  the  velocity  of 
the  pile  at  each  instant  of  its  movement,  and  the  amount  of 
compression  suffered  by  the  head  of  the  pile  from  the  blow  of  the 
hammer,  it  was  found  that  on  the  average  the  penetration,  meas- 
ured from  the  deepest  point,  varies  practically  as  the  square  of 
the  time  measured  from  the  final  instant.  The  autographic 
records  showed  also  that,  in  the  majority  of  cases,  the  final  mag- 
nitude of  the  force  acting  on  the  pile  is  the  same  as  its  initial 
magnitude  when  the  pile  and  hammer  move  together;  and 
prove  conclusively  that  the  hammer  remains  in  contact  with 
the  pile  until  the  motion  of  the  latter  has  ceased. 

Small- sized  experiments  on  pressing  sticks  with  blunt\ips 
into  sand  and  other  kinds  of  earth,  as  well  as  observations  of 
regular  piles,  show  that  a  conical  mass  is  formed  at  the  tip  and 
pushed  along  while  curved  flow  lines  of  earth  appear  as  the 
material  is  pushed  aside  and  compressed.  The  extent  of  the 
movement  depends  upon  the  compressibility  of  the  earth. 


14  TIMBER  PILES   AND  DRIVERS  CHAP.  I 

Often  some  of  the  material  near  the  sides  of  the  pile  will  move 
upward  slightly.  It  is  thus  seen  that  the  supporting  power  of 
the  ground  penetrated  is  one  of  the  elements  which  determines 
the  load  which  a  pile  can  bear.  In  most  cases  this  supporting 
power  of  the  ground  increases  more  or  less  with  the  depth,  and 
hence  the  load  depends  upon  the  total  depth  of  penetration. 
Sometimes  the  larger  part  of  the  superimposed  load  is  trans- 
mitted by  the  pile  through  its  foot  to  a  hard  substratum,  and 
therefore  acts  like  a  column.  When  the  pile  is  supported 
entirely  by  the  frictional  resistance  between  its  sides  and  the 
earth,  the  load  is  transmitted 'to  a  deep  ground  level  in  a  conoid 
of  pressure  through  the  earth  above  it.  Usually  these  two 
methods  of  transferring  a  load  from  a  pile  to  the  earth  act 
together  in  varying  proportions. 

ART.  6.     PILE-DRIVERS 

A  pile-driver  is  a  machine  for  driving  piles.  Its  characteris- 
tic feature  consists  of  the  leads,  which  are  upright  parallel  mem- 
bers to  support  the  sheaves  used  to  hoist  the  hammer  and  piles, 
and  to  guide  the  hammer  in  its  movement.  The  leads  are  held 
in  position  by  being  framed  with  back  stays  and  other  bracing 
into  the  form  of  a  tower  supported  on  horizontal  sills.  In  a 
standard  form  of  contractors'  pile-driver  the  bed  frame  con- 
taining the  sills  is  extended  back  far  enough  to  support  the  hoist- 
ing engine  and  boiler,  and  the  whole  outfit  is  mounted  on  rollers 
as  illustrated  in  Fig.  6a. 

Pile-driver  towers  are  constructed  either  of  timber  or  steel, 
and  are  built  in  a  variety  of  forms  for  different  purposes,  or 
conditions.  Rungs  are  attached  to  the  rear  inclined  posts,  or 
back  stays  of  the  tower,  to  form  a  ladder.  The  bracing  consists 
of  horizontal  and  diagonal  members.  In  the  figure  two  long 
diagonal  braces  are  shown  in  addition  to  the  diagonals  in  each 
panel.  Sometimes  the  long  diagonals  are  omitted  and  only 
short  diagonals  are  placed  in  every  panel,  while  in  the  smaller 
towers  all  diagonals  may  be  omitted.  Occasionally  the  lower 
diagonals  are  extended  over  two  panels,  or  long  diagonals  may 


ART.  6 


PILE-DRIVERS 


Head 

Block 


ollers  — -• 

FIG.  6a. — A  Standard  Type  of  Contractor's  Pile-Driver 


1 6  TIMBER   PILES   AND   DRIVERS  CHAP.  I 

be  employed  without  any  short  ones.  The  tower  is  braced 
laterally  either  by  guy  ropes  attached  to  the  rings  near  its  top  or 
by  long  inclined  posts,  or  wind  braces,  in  which  case  the  bed 
frame  is  generally  widened  to  support  these  braces.  Leads  as 
long  as  100  feet  and  i  inch  under  the  head-block  have  been 
built.  See  also  Fig.  620,. 

By  the  addition  of  roller  bearings  a  driver  may  be  moved  for- 
ward, backward,  and  sidewise.  When  it  is  mounted  on  a 
turntable  it  is  called  a  swiveling  pile-driver,  and  combines  swing- 
ing to  the  right  or  left  with  the  motions  noted  in  the  previous 
sentence,  the  movement  sidewise  being  made  however  by  chang- 
ing the  rollers.  The  inner  faces  of  wooden  leads  are  protected 
by  channel-iron  liners,  in  order  to  reduce  friction  and  wear. 

A  driver  intended  to  be  used  in  excavations  to  drive  piles 
below  the  level  of  its  supporting  track,  sometimes  has  rigid 
detachable  leads  which  extend  to  the  required  depth.  A  better 
arrangement  consists  in  the  use  of  telescopic  leads  which  slide 
inside  of  the  stationary  leads,  and  are  handled  by  an  extra  line 
to  a  third  hoisting  drum.  By  this  means  piles  may  be  driven 
without  the  aid  of  a  follower  in  deep  trenches  or  through  con- 
tracted openings,  or  in  the  bottoms  of  cofferdams  containing  a 
large  amount  of  internal  bracing.  Floating  pile-drivers 
mounted  on  scows  have  had,  in  exceptional  cases,  loo-foot 
telescopic  extension  leads  working  within  zoo-foot  fixed  leads. 
With  such  equipment  it  has  been  possible  to  drive  piles  35  to  40 
feet  below  the  water  surface  with  the  aid  of  a  follower  that  was 
thus  guided  at  its  lower  end  as  well  as  at  its  upper  one.  Hang- 
ing leads,  which  can  also  be  used  for  the  same  purpose  as  exten- 
sion leads,  are  often  used  in  connection  with  ordinary  derricks 
or  cranes. 

ART.  7.     TRACK  PILE-DRIVERS 

Pile-drivers  of  recent  design  for  railroad  service  have  been 
developed  to  a  high  degree  of  efficiency.  In  the  report  of  the 
Committee  on  Wooden  Bridges  and  Trestles  of  the  American 
Railway  Engineering  Association  in  1911  (see  Proceedings,  vol. 
12,  part  i,  page  290),  are  contained  the  following: 


ART.  7  TRACK  PILE-DRIVERS  17 

DESIRABLE  FEATURES  OF  A  TRACK  PILE-DRIVER 

(i)  Steam-hammer.  To  secure  greater  rapidity  in  driving 
and  with  less  injury  to  the  pile  than  that  secured  by  the  drop- 
hammer.  (2)  Water- jet  apparatus.  (3)  Turntable  allowing 
practically  a  complete  rotation.  In  most  cases  the  work  can  be 
done  from  either  side,  and  in  many  of  the  remaining  cases  it  is 
possible  to  foresee  the  nature  of  the  work  and  to  head  the 
driver  in  the  proper  direction  at  the  nearest  Y  or  turntable. 
Sometimes,  however,  turning  facilities  may  be  far  distant,  or  a 
pile-driver  may  be  caught  between  two  washouts  when  it 
becomes  essential  to  be  able  to  turn  the  machine  to  perform  the 
work  at  both  places.  (4)  Swinging  leads.  The  leads  require 
an  efficient  rigging  to  permit  driving  piles  with  a  batter  in  either 
direction.  When  driving  across  the  track  on  such  work  as 
driving  bents  for  an  adjacent  track,  it  is  convenient  to  be  able 
to  drive  with  the  leads  not  fully  raised,  so  as  to  secure  the  proper 
batter.  (5)  Self-propelling  mechanism.  The  greater  the  tract- 
ive force  and  speed  the  more  independent  is  the  pile-driver  from 
locomotive  service.  They  should  preferably  be  sufficient  to  dis- 
pense with  a  locomotive  except  for  long  hauls.  (6)  Restricted 
projection  on  the  side  opposite  the  leads  when  swung 
across  the  track  and  without  unnecessary  weight.  (7)  High- 
speed power  service  for  raising  the  leads.  On  a  main  line  it  is 
frequently  possible  to  drive  only  one  or  two  piles  before  running 
to  a  siding.  In  some  cases  the  character  of  this  apparatus  to 
raise  the  leads  determines  whether  a  single  pile  can  be  driven 
between  trains  or  will  delay  a  train.  (8)  Adequate  overhang. 
To  enable  machines  to  drive  piles  as  far  ahead  of  the  leading 
wheels  and  as  far  sidewise  as  possible.  On  work  for  double- 
tracking  the  sidewise  reach  should  be  sufficient  to  drive  a  bent 
on  the  new  track  from  a  position  on  the  old  track.  (9)  Facili- 
ties for  driving  below  the  track.  (10)  Ability  to  shift  the  ham- 
mer when  the  leads  are  down,  (n)  No  obstructions  in  the 
view  of  the  engineman  and  niggerhead  operator.  (12)  Length 
of  leads.  To  accommodate  the  longest  piles  practicable.  (13) 
Strength  and/igidity  of  supports  for  leads  and  hammer.  They 


i8 


TIMBER   PILES   AND   DRIVERS 


CHAP.  I 


FIG.  "jd. — Locomotive  Crane  Used  as  a  Traveler  and  Pile- Driver  in 
Building  a  Pile  Trestle. 

The  25-foot  leads  swing  freely  on  the  bolt  by  which  they  are  suspended  from  the 
boom;  when  driving  they  are  braced  by  struts  to  some  of  the  finished  work.  Cross 
pieces  on  the  back  of  the  leads  and  an  iron  bar  placed  across  the  front  on  two  hooks 
at  the  bottom  of  the  leads  hold  the  pile  in  position.  The  drop  hammer  is  operated 
by  the  regular  hoisting  rope,  and  the  same  rope  is  used  to  hoist  the  pile  into  the 
leads,  the  hammer  meantime  being  held  at  the  top  of  the  guides  by  a  bolt. 


ART.  7  TRACK   PILE -DRIVERS  1 9 

should  be  adequate  to  handle  the  hammer  and  the  heaviest 
wooden  pile  without  damage.  It  is  now  becoming  important 
to  be  able  to  handle  concrete  piles.  (14)  Stability.  The 
driver  while  standing  on  its  own  wheels,  without  any  jacks 
or  special  supports,  should  be  able  to  pick  up  and  drive  a  pile 
in  any  position  within  its  reach.  (15)  Flush  ends.  For 
convenience  of  transportation  in  freight  trains,  no  part  project- 
ing beyond  the  drawheads.  Otherwise  an  idler  is  required 
which  then  may  be  used  as  a  tool  car.  (16)  No  lengths  of 
steam  hose  that  might  be  replaced  by  pipe. 

No  single  make  or  design  of  driver  has  incorporated  every  one 
of  these  desirable  features.  Those  which  come  nearest  to  doing 
so  are  not  of  the  combination  type  but  are  designed  especially 
for  exclusive  use  as  pile-drivers.  In  different  makes  the  reach 
ranges  from  15  to  21  feet  ahead  of  the  wheel  base,  the  reach  side- 
ways from  20  to  33  feet  from  center  of  track,  while  the  longer 
leads  are  from  40  to  47  feet.  Some  drivers  are  equipped  with 
both  steam-  and  drop-hammers  and  the  best  ones  have  a  water- 
jet  outfit.  The  turntable  is  usually  on  top  of  the  car  body 
but  in  one  case  a  hydraulic  turntable  is  provided  which  takes 
bearing  on  the  track,  raises  and  turns  the  entire  car  (Fig.  70). 
Those  which  are  self-propelling  have  a  speed  from  8  to  25 
miles  per  hour. 

In  one  typical  form  the  aim  has  been  to  combine  the  functions 
of  a  pile-driver  with  those  of  a  steam-derrick  car  in  the  erection 
of  small  bridges,  the  maintenance  of  bridges  and  culverts,  pulling 
down  temporary  structures  and  old  bridges,  or  clearing  up  a 
wreck.  A  boom  is  therefore  provided  of  sufficient  capacity  for 
such  work.  In  some  instances  it  is  placed  in  front  of  the  leads 
when  in  use,  while  in  others  the  boom  always  remains  in  place, 
being  connected  by  blocks  and  tackle  to  a  transverse  frame  and 
mast,  the  pile  driving  being  done  by  leads  hanging  from  the 
boom.  In  transit  the  boom  is  down  and  extends  over  the  length 
of  a  flat  idler  car  coupled  ahead.  In  another  typical  form  the 
leads  and  their  supporting  truss  and  braces  are  replaced  by 
other  appliances  to  convert  it  into  a  locomotive  crane  or 
excavator. 


20 


TIMBER   PILES    AND   DRIVERS 


CHAP.  I 


ART.  8.    THE  DROP  PILE-HAMMER 

A  drop-hammer  is  one  which  is  raised  by  means  of  a  rope  and 
then  allowed  to  drop.  It  consists  of  a  solid  casting  with  jaws  on 
each  side  which  fit  into  the  guides  of  the  pile-driver  leads,  with 
a  pin  near  the  top  for  the  attachment  of  the  rope  or  of  the  nip- 
pers, and  with  a  broad  base  on  which  it  strikes  the  pile. 

Fig.  Sa  shows  a  drop-hammer  of  modern  design  with  all  cor- 
ners rounded.  It  is  made  as  long  as  practicable  to  increase  the 
bearing  in  the  leads,  while  the  jaws  have 
as  little  play  as  possible  between  the 
leads  and  hammer  to  reduce  the  jar  on 
the  driver  when  the  pile  is  struck.  The 
form  is  arranged  to  have  its  center  of 
gravity  as  low  as  possible.  When  the 
hammer  is  to  hit  the  head  of  the  pile 
directly,  its  base  is  made  slightly  con- 
cave, but  when  a  pile  cap  is  employed, 
as  is  done  in  the  best  practice,  the  base 
is  made  flat. 

When  the  hammer  is  to  have  a  free 
fall,  as  may  be  required  on  test  piles  or 
for  very  light  hammers  raised  by  horse 
power,  the  pin  is  triangular  in  section 

with  its  lower  face  horizontal,  to  engage  the  'nippers'  auto- 
matically. The  upper  ends  of  the  nippers  are  curved  so  that 
when  the  trip  is  reached,  they  are  drawn  together  and  thus 
release  the  hammer  for  its  drop  on  the  pile.  When  the  ham- 
mer is  to  be  raised  by  a  hoisting  drum  with  a  friction  clutch,  a 
round  pin  is  used  to  which  the  line  is  attached  directly.  The 
latter  method  affords  the  following  advantages  for  regular 
work:  More  rapid  operation;  facility  in  regulating  the  height 
of  drop;  and  avoiding  the  danger  of  losing  the  hammer  if  it 
should  pass  out  of  the  leads. 

The  weight  of  drop-hammers  most  generally  used  in  American 
practice  to  drive  timber  piles  ranges  from  about  2000  to  3800 
pounds.  For  posts  and  very  small  piles  the  weight  runs  as  low 


FIG.  8a. — Drep- Hammer. 


ART.  9  THE   STEAM   PILE-HAMMER  21 

as  500  pounds,  while  for  heavy  construction  requiring  very  long 
piles  it  runs  as  high  as  5200  pounds.  For  very  light  service  a 
heavy  block  of  oak  wood  is  sometimes  employed.  The  weight 
of  drop-hammers  to  be  adopted  depends  upon  the  weight  of  the 
piles  and  the  character  of  the  ground  to  be  penetrated.  The 
relation  of  the  weight  and  fall  of  the  hammer  to  the  bearing 
power  of  piles  and  to  success  in  securing  adequate  total  penetra- 
tion without  injury  to  timber  piles  is  discussed  in  Art.  27. 
The  weight  of  hammers  to  drive  concrete  piles  is  referred  to 
in  Art.  48. 

ART.  9.     THE  STEAM  PILE-HAMMER 

A  steam-hammer  is  one  which  is  automatically  raised  and 
dropped  a  comparatively  short  distance  by  the  action  of  a  steam 
cylinder  and  piston  supported  in  a  frame  which  follows  the  pile. 
It  was  invented  in  England  by  JAMES  NASMYTH  in  1845,  an<3 
was  first  used  on  October  6,  1846,  to  drive  piles  for  a  bridge 
foundation.  One  type  of  steam-hammers  has  been  built  in 
this  country  since  1875  and  after  various  improvements 
has  continued  in  use,  being  known  at  present  as  the 
Warrington  hammer. 

Steam-hammers  are  of  two  general  classes  single  acting  and 
double  acting.  In  the  former  and  older  class  the  steam  pressure 
is  applied  to  raise  the  striking  part  of  the  hammer,  while  it  falls 
by  gravity.  The  force  of  the  blow  depends  upon  the  length  of 
stroke  and  the  movable  weight,  the  number  of  blows  depending 
upon  the  steam  pressure.  In  the  latter  class  the  steam  pressure 
raises  the  hammer  and  also  reinforces  the  action  of  gravity  dur- 
ing its  descent,  the  force  of  the  blow,  as  well  as  the  rapidity  of 
action,  being  functions  of  the  pressure.  The  latter  apparatus  is 
more  compact,  lighter  and  operated  with  greater  rapidity.  The 
Warrington  and  Cram  hammers  are  single  acting,  while  the 
Arnott,  Industrial  Works,  New  Monarch,  Goubert,  and  McKier- 
nan-Terry  hammers  are  double  acting.  Another  classification 
may  be  based  upon  whether  the  striking  part  is  attached  to  a 
movable  piston  or  to  a  movable  cylinder.  The  Warrington, 


22 


TIMBER   PILES   AND   DRIVERS 


CHAP.  I 


Arnott,  New  Monarch,  and  McKiernan-Terry  have  the  former 
arrangement,  while  the  Cram,  Industrial  Works,  and  Goubert 
have  the  latter.  The  latter  arrangement  is  also  incorporated, 
however,  in  the  McKiernan-Terry  hammer  since  it  contains  an 
auxiliary  fixed  piston  which  operates  in  a  cylinder  bored  out  of 
the  upper  end  of  the  main  piston.  This  novel  feature  forms  a 
device  to  accelerate  and  intensify  the  down-stroke. 


FIG.  ga. — Warrington. 


FIG.  96. —  Cram. 

Steam  Pile- Hammers. 


FIG.  qc. — Goubert. 


The  following  table  gives  weights,  dimensions  and  other 
data  for  the  largest  regular  size  of  hammer  for  each  of  six  differ- 
ent makes.  It  is  noted  that  in  the  double-acting  hammers  the 
weight  of  striking  parts  is  only  about  one-half  to  one-fourth  as 
great  as  in  the  single-acting  ones.  The  table  also  indicates  the 
steadily  increasing  number  of  blows,  as  well  as  the  reduced 
height,  thus  requiring  less  space  in  the  leads.  The  piston  speed 
is  nearly  uniform.  The  Arnott  and  the  McKiernan-Terry  ham- 


ART.  9 


THE    STEAM   PILE-HAMMER 


mers  may  also  be  operated  by  compressed  air. 
steam-hammer  is  illustrated  in  Fig.  6a. 


The  Arnott 


LARGEST  SIZES  OF  VARIOUS  STEAM  PILE-HAMMERS 


Trade  designation 

Warrington 

B 

S 

Arnott 

Industrial 
Works 

New 
Monarch 

Goubert 

McKiernan- 
Terry 

Size  number.  . 

I 

B 

o 

I 

.    -2 

Total  weight  in  pounds  

10  150 

8  400 

12  IOO 

6  400 

7  ooo 

<  OOO 

8  IOO 

Weight  of  striking  part,  pounds. 
Total  height  in  inches 

5000 

i?o 

5  5oo 
14.4 

2  550 

118 

i  900 
lie 

i  SOQ 

QO 

I  500 
76 

I  250 

77 

Diameter  of  cylinder,  inches.  .  .  . 
Stroke  in  inches 

13-5 

42 

i5 

4O 

10.5 

24 

8 

24 

9 

14 

'g 

14 

15 
12 

Total  downward  force,  pounds.  . 
Number  of  blows  per  minute  
Boiler  pressure,  Ibs  per  sq  in 

5  ooo 

60 

SSoo 
60 

7  800 

IOO 

80 

6  175 

IOO 
IOO 

6  200 

125 
80 

6080 

ISO 
80 

7  loo 

200 
80 

Boiler  required,  HP  

40 

20—30 

CO 

(TO 

2C 

60 

The  total  weights  of  the  smallest  sizes  are  respectively  1350 
1000,  365,  750,  950,  and  175  pounds.  The  number  of  blows 
per  minute  for  the  double-acting  hammers  for  the  same  sizes  are 
300,  350,  200,  and  500.  Generally  the  lightest  hammers  are 
used  for  light  sheet-piling  only.  Additional  data  may  be  found 
in  the  illustrated  catalogues  published  by  the  manufacturers. 

During  the  operation  of  driving,  the  steam-hammer  and  its 
frame  rest  upon  the  pile,  the  head  of  which  is  trimmed  to  fit 
into  the  recessed  or  open  base  of  the  frame.  The  frame  has 
channel  or  angle  guides  on  the  sides  which  engage  the  leads  of  the 
driver.  The  frame  in  turn  guides  the  hammer  in  its  movement, 
and  in  several  makes  entirely  encases  it.  While  the  weight  of 
the  striking  parts  is  only  a  fraction  of  the  total  weight,  the  extra 
dead  weight  of  the  frame  helps  to  keep  the  pile  in  motion  after 
it  is  started  by  the  blow.  Generally  the  blows  follow  each  other 
so  rapidly  that  the  pile  is  in  continuous  motion.  The  limited 
vibration  thus  developed  in  the  pile  is  also  an  aid  in  securing  its 
penetration,  particularly  in  ground  containing  a  large  percent- 
age of  sand  which  otherwise  offers  considerable  resistance.  The 
vibration  is  limited  by  the  weight  which  constantly  rests  upon 


TIMBER  PILES   AND  DRIVERS 


CHAP.  I 


the  pile.  The  effect  of  the  short  quick  blow  in  securing  pene- 
tration is  analogous  to  the  method  of  driving  an  ordinary  pin 
into  a  block  of  lead  by  many  light  taps  with  a  very  small  ham- 
mer, which  could  not  be  done  by  fewer  but  heavier  blows. 


FIG.  gd. — New  Monarch.    PIG.  ge. — McKiernan- Terry.     FIG.  gf. — Industrial  Works. 
Steam  Pile-Hammers. 


ART.  10.    ADVANTAGES  OF  STEAM-HAMMERS 

The  following  selected  records  of  actual  experience  are  pre- 
sented in  order  to  indicate  the  relative  values  of  steam-  and 
drop-hammers  when  used  under  practically  the  same  conditions. 
The  interests  of  good  practice  would  be  materially  aided  if  more 
tests  of  this  kind  were  made  under  a  wide  range  of  conditions. 

In  driving  piles  for  cylinder  piers  20  feet  in  diameter  for 
a  bridge  on  the  Norfolk  and  Western  Railroad,  at  Norfolk, 
Va.,  the  piles  in  one  cylinder  were  driven  by  a  3300-pound 
drop-hammer  with  a  fall  of  10  feet,  while  those  in  the  twin 
cylinder  of  the  same  pier  33  feet  away  and  in  the  nearest  cylinder 


ART.  10  ADVANTAGES   OF   STEAM-HAMMERS  25 

of  the  next  pier,  44  feet  distant,  were  driven  by  a  steam-hammer 
with  striking  parts  weighing  3000  pounds,  a  total  weight  of  6000 
pounds,  a  normal  stroke  of  36  inches  and  an  effective  fall  of  30 
inches.  The  following  record  relates  only  to  the  averages  for 
the  first  six  piles  driven  in  each  cylinder  respectively.  In  the 
first  cylinder  the  average  penetration  under  the  last  blows  was 
|  inch,  and  for  each  of  the  other  cylinders  the  average  penetra- 
tion under  the  last  100  blows  was  7  inches  or  practically  14 
blows  per  inch.  The  total  penetrations  averaged  28,  36,  and 
26  feet  respectively  for  the  three  cylinders.  The  drop-hammer 
broomed  the  heads  of  the  piles  and  no  increase  in  penetration 
was  secured  by  increasing  the  drop  above  10  to  15  feet.  With 
the  steam-hammer  no  brooming  occurred  and  the  full  force  of 
the  blow  was  effective  at  all  stages  of  the  driving.  The  piles 
were  driven  in  about  38  feet  of  water,  about  16  feet  of  the  soft 
silt  having  been  dredged  out  so  that  all  the  penetration  secured 
was  through  firm  blue  mud  and  sand  in  layers  of  varying 
thickness. 

On  the  Chicago  and  Eastern  Illinois  Railroad  the  perform- 
ances of  a  steam-hammer  and  drop-hammer  were  compared  by 
using  them  on  the  same  pile,  changing  the  hammer  in  the  leads 
as  quickly  as  possible.  The  former  had  a  total  weight  of  5170 
pounds,  and  striking  parts  of  2840  pounds,  while  the  latter 
weighed  2900  pounds.  The  former  had  a  drop  of  28  inches, 
and  the  latter  of  32  feet.  With  the  steam-hammer  66  blows 
produced  i  foot  of  penetration  in  i  minute,  and  another  foot 
by  83  blows  in  if  minutes;  the  next  foot  of  penetration  was 
obtained  by  the  drop-hammer  with  12  blows  in  2  minutes, 
and  the  following  4  feet  respectively  by  12,  10,  10,  and  12  blows 
in  2,  2,  3^,  and  i\  minutes;  the  steam-hammer  being  replaced 
caused  the  next  foot  of  penetration  with  203  blows  in  3  minutes, 
and  the  following  9  feet  by  341  blows  in  5  minutes. 

In  driving  piles  for  a  large  wharf  and  warehouse  at  Pensa- 
cola,  Fla.,  requiring  7000  piles,  two  piles  75  feet  long  were 
driven  3  feet  apart,  one  by  a  drop-hammer  and  the  other  by  a 
steam-hammer.  The  former  was  driven  by  120  blows  in  50 
minutes,  dropping  the  hammer  from  the  top  of  the  7 5 -foot  leads; 


26  TIMBER   PILES   AND   DRIVERS  CHAP.  I 

and  the  latter  by  130  blows  in  90  seconds.  As  should  be  ex- 
pected under  such  abnormally  high  falls  the  former  pile  was 
broomed  for  a  depth  of  over  3  feet  at  the  head,  while  the  one 
driven  with  the  steam-hammer  was  not  broomed  at  all.  The 
piles  were  creosoted  and  cost  40  cents  per  linear  foot  delivered. 

On  the  North  River  at  New  York  City  piles  from  55  to  60 
feet  long  were  driven  from  43  to  50  feet  below  low  water  through 
a  lo-foot  layer  of  cobble  stones,  and  layers  of  very  fine  sand, 
coarse  gravel,  and  sand  gravel,  as  shown  by  test  borings.  To 
drive  12  piles  in  10  hours  by  a  crew  of  10  men  was  regarded  as  a 
good  day's  work,  an  average  of  175  blows  with  a  33oo-pound 
drop-hammer  falling  10  feet  being  required,  at  a  rate  of  15  blows 
per  minute.  With  a  crew  of  2  or  3  men  less,  18  piles  per  day 
could  be  driven  by  a  steam-hammer  and  braced,  some  of  the 
piles  requiring  over  1200  blows  at  the  rate  of  60  per  minute 
without  showing  any  sign  of  brooming.  The  hammer  had  a 
total  weight  of  8400  pounds,  and  a  striking  weight  of  4000 
pounds. 

A  contractor  endeavored  to  drive  some  45-foot  piles  through 
sand,  gravel,  and  boulders,  for  bridge  piers  on  the  New  York, 
Westchester  and  Boston  Railroad  at  Pelham,  N.  Y.,  using  a 
3ooo-pound  drop-hammer  falling  20  to  40  feet,  but  did  not 
succeed.  A  steam-hammer  was  then  obtained  with  a  3000- 
pound  striking  weight,  which  secured  the  full  penetration  with- 
out brooming  or  splitting  any  piles. 

The  following  advantages  are  claimed  for  the  use  of  the 
steam-hammer  by  those  who  have  also  had  experience  with  the 
drop-hammer :  (i)  The  pile  is  held  in  position  and  guided  more 
firmly  while  driving,  thus  keeping  the  pile  from  dodging,  or 
getting  out  of  line,  and  avoiding  the  labor  of  toggling.  (2) 
Serious  damage  to  the  pile  such  as  brooming,  splitting,  etc.,  is 
avoided.  Hence  piles  of  softer  wood  may  be  employed.  (3) 
Extra  time  and  cost  for  the  use  of  a  ring  on  the  pile  head  is 
saved.  (4)  The  driving  is  equally  effective  for  any  position 
of  the  pile  head  in  the  leads.  (5)  A  pile  may  be  driven  several 
feet  (7  or  8  feet  with  some  hammers)  below  the  bottom  of  the 
fixed  leads  without  the  use  of  extension  leads.  A  few  feet  may 


ART.  ii  RINGS,   CAPS,   AND   FOLLOWERS  27 

often  be  saved  in  cut-off  by  thus  driving  below  the  elevation 
of  rail.  (6)  When  driving  into  soft  material  or  into  sand,  the 
rapidity  of  action  keeps  the  pile  in  motion  and  prevents  the 
earth  from  recompacting  around  the  pile  until  the  driving  ceases, 
thus  reducing  the  frictional  resistance.  (7)  More  piles  can  be 
driven  in  a  given  time  and  often  with  a  smaller  crew.  (8)  The 
steam-hammer  has  been  used  effectively  in  places  and  under  con- 
ditions where  it  was  found  to  be  impossible  to  use  a  drop-ham- 
mer successfully.  This  relates  to  cases  of  limited  head  room 
as  well  as  to  difficult  subsurface  conditions.  (9)  Less  injury 
is  caused  to  adjacent  foundations,  and  less  breaking  of  glass 
and  plastering  in  adjoining  buildings.  (10)  The  leads  last 
about  three  or  four  times  as  Jong  as  when  a  drop-hammer  is 
used,  (n)  On  track  pile-drivers  less  injurious  strains  are  caused 
in  the  car  and  machinery,  thus  reducing  the  cost  of  mainte- 
nance. (12)  Although  the  first  cost  of  the  steam-hammer  is 
much  greater  the  total  cost  of  driving  is  reduced. 

The  teaching  of  experience  is  indicated  by  the  fact  that  in 
the  city  of  Chicago,  where  perhaps  more  piles  are  driven  for 
foundations  than  in  any  other  place  in  the  United  States, 
steam-hammers,  are  used  almost  exclusively.  Those  who  have 
had  considerable  practice  in  the  use  of  both  kinds  of  pile- 
hammers  do  not  as  a  rule  wish  to  go  back  to  the  drop-hammer. 
Exceptional  cases  have  been  reported  in  which  a  steam-hammer 
has  been  unable  to  force  a  pile  through  a  hard  crust.  A  drop- 
hammer  may  succeed  in  such  a  case  because  of  its  heavier  blow, 
but  it  is  more  likely  to  break  the  pile.  Perhaps  a  pointed  shoe 
may  be  needed  on  the  pile,  or  a  charge  of  dynamite,  or  a 
dredge.  Sometimes  more  caution  is  needed  with  a  track  driver 
when  the  track  is  out  of  level  if  the  heavier  steam-hammer  is 
near  the  top  of  the  leads. 

Art.  ii.     RINGS,  CAPS,  AND  FOLLOWERS 

It  is  important  to  cut  off  square  the  butt  of  a  pile,  so  that 
the  impact  of  the  hammer  may  be  distributed  uniformly  over 
the  surface.  Since  the  butt  tends  to  change  its  position  slightly 
in  the  leads  during  driving,  it  has  been  found  advantageous  by 


28  TIMBER   PILES   AND   DRIVERS  CHAP.  I 

experience  to  make  the  lower  surface  of  the  drop-hammer 
slightly  concave.  This  provision  counteracts  the  tendency  to- 
ward lateral  movement  of  the  pile  to  some  degree.  When  the 
pressure  on  any  fibers  exceeds  their  ultimate  resistance  in  com- 
pression they  will  yield  by  bending,  buckling,  or  crushing, 
after  their  adhesion  to  adjacent  fibers  is  destroyed.  When 
the  fibers  are  once  broken  down  every  blow  of  the  hammer 
tends  to  injure  the  fibers  further  down.  As  wooden  fibers 
are  far  more  compressible  when  a  force  is  applied  on  their 
sides  instead  of  their  ends,  the  bruised  head  of  the  pile  thus 
becomes  more  elastic,  and  acts  somewhat  like  a  spring  or  cushion. 
When  the  height  of  fall  for  the  hammer  exceeds  a  certain  value, 
a  part  of  its  energy  is  expended  in  destructive  work  like  that 
just  indicated,  leaving  less  for  useful  work,  reducing  its  ef- 
ficiency in  forcing  the  pile  to  penetrate  the  ground.  This 
breaking  down  of  the  fibers  is  called  'brooming.'  The  fall  of 
the  hammer  may  be  so  great  that  nearly  all  of  the  energy  is 
used  up  in  brooming  the  pile.  The  relation  of  the  weight  of  the 
hammer  and  the  height  of  its  fall  to  the  bearing  power  of  a 
pile  is  discussed  in  Art.  27. 

It  is  often  found  that  no  increase  in  penetration  is  secured 
by  increasing  the  fall  or  drop  above  10  to  15  feet.  It  is  possible 
to  estimate  approximately  the  loss  of  energy  due  to  brooming 
by  comparing  the  number  of  blows  required  per  foot  of  pene- 
tration before  and  after  cutting  off  the  broomed  top.  From 
the  record  of  a  pile  driven  by  a  steam-hammer,  under  the 
direction  of  D.  J.  WHITTEMORE,  it  is  observed  that  in  driving 
the  pile  from  the  i2th  to  the  22d  foot  of  penetration,  4682  blows 
were  struck  or  an  average  of  468  blows  per  foot.  Immediately 
after  cutting  off  the  broomed  top  at  two  different  times,  only 
275  and  213  blows  respectively  were  required  to  drive  the  pile 
the  next  foot.  Their  average  of  244  blows  indicates  the  number 
required  under  the  condition  of  a  sound  head,  and  accordingly 
it  appears  that  on  the  average  only  about  52  percent  of  the 
available  energy  was  consumed  in  securing  the  penetration 
of  the  pile.  The  loss  in  this  case  is  considered  excessive.  The 
progressive  effect  of  brooming  is  shown  in  the  number  of  blows 


ART.  ii  RINGS,    CAPS,    AND   FOLLOWERS  2Q 

required  for  the  zoth  to  the  i4th  foot  of  penetration  respectively: 

73>  I09'  J53>  259>  684- 

The  brooming  and  splitting  of  pile  heads  varies  for  different 
kinds  of  wood.  The  record  of  pile  driving  for  the  foundations 
of  a  building  in  Chicago,  shows  that  for  pine  12.5  percent  of 
the  heads  were  crushed  and  5  percent  broken;  for  gum,  7  per- 
cent crushed  and  0.6  percent  broken;  for  oak,  5  percent  crushed 
and  0.8  percent  broken;  for  hickory,  3  percent  crushed  and  none 
broken;  and  for  basswood,  8  percent  crushed.  In  several  of 
the  oak  piles  the  sapwood  and  heart  separated,  the  heart  core 
being  driven  through  the  shell.  A  cast-iron  cap  was  used  in 
driving,  but  in  spite  of  this,  an  average  of  8  percent  of  the  heads 
were  crushed  or  split;  but  when  it  is  considered  that  the  fall 
of  the  hammer  for  each  pile  was  permitted  to  reach  the  magni- 
tude of  35  and  40  feet  when  the  driving  ceased,  it  is  surprising 
that  these  percentages  were  not  larger.  The  penetration  at 
the  last  blow  averaged  3  inches.  The  percentages  of  piles  used 
on  the  work  of  the  different  species  of  wood  named  above  and 
in  the  same  order  were  22,  32,  21,  15,  and  7  respectively. 

The  crushing  of  the  fibers  is  frequently  followed  by  the 
splitting  of  the  pile  head.  This  tendency  is  promoted  by  fail- 
ing to  cut  off  enough  of  the  butt  as  it  comes  from  the  forest 
to  cover  the  entire  section  area  of  the  pile,  for  if  the  hammer 
hits  only  one-half  of  the  area  it  will  force  that  part  down  into 
the  head  and  split  it. 

To  prevent  splitting  and  to  reduce  brooming,  the  head  may 
be  hooped  by  a  pile  ring.  The  sizes  range  from  2  by  f  to  4  by 
i  inches.  The  diameters  vary  to  suit  different  sizes  of  pile. 
They  are  .made  of  the  best  quality  of  wrought  iron  that  can 
be  obtained.  Rings  of  the  best  bar  iron  usually  last  to  drive 
50  oak  piles  or  200  cedar  piles;  those  of  the  best  hammered 
iron  for  75  oak  piles  or  300  cedar  piles.  Rings  made  out  of 
old  car  axles  have  been  used  for  250  oak  or  6000  cedar  piles. 

In  fitting  the  ring  the  pile  is  neatly  chamfered  down  at 
least  5  inches  from  the  end  so  that  the  ring  will  just  catch 
on;  a  blow  of  the  hammer  puts  it  into  place.  To  remove  the 
ring  a  cant-hook  or  pevee  is  used,  the  pile  line  being  fastened 


TIMBER   PILES   AND   DRIVERS 


CHAP.  I 


—  -Hammer 


_ 

on  Block 


to  its  end  to  apply  steam  power.  If  the  pile  brooms  too  much 
in  spite  of  the  ring,  the  recognized  remedy  is  to  saw  off  the 
broomed  part,  so  as  to  present  a  solid  surface  to  the  hammer 
and  put  the  ring  on  again. 

A  more  effective  and  less  expensive  method  of  protecting  the 
head  of  a  timber  pile  from  brooming  and  splitting  is  the  use  of 

a  pile  cap  as  shown  in  Fig. 

..-Lead)-. 

na.  It  consists  of  a  cast- 
ing with  a  tapered  recess 
above  and  below.  The 
chamfered  head  of  the  pile 
fits  into  the  lower  recess 
and  a  short  cushion  block 
of  hard,  tough  wood  is 
fitted  into  the  upper  one. 
The  block  is  frequently 
provided  with  an  iron 
hoop  or  ring  around  its 
top.  The  cap  has  jaws  on 
the  sides  like  the  hammer 
which  engage  the  leads, 
and  hence  the  head  of  the 
pile  is  held  in  position  and  guided  while  driving.  After  the 
pile  is  driven  the  cap  is  hooked  to  the  hammer  by  ropes  and  pins 
and  raised  with  it.  While  the  cap  protects  the  pile  head  the 
short  cushion  block  requires  frequent  renewal  since  it  gets  the 
direct  impact  of  the  hammer.  Sometimes  a  rope  mat  is  placed 
on  top  to  protect  it.  White,  live  or  swamp  oak,  rock  maple, 
and  blue  gum  have  given  good  service  for  cushion  blocks. 

When  both  drop-  and  steam-hammers  are  used  on  the  same 
work  it  is  often  found  that  the  drop-hammer  causes  brooming 
when  the  steam-hammer  gives  no  indication  of  it.  In  hard 
driving,  however,  it  becomes  important  to  protect  the  pile  head. 
Sometimes  this  is  done  by  spiking  a  flat  steel  plate  on  the  pile 
to  receive  the  blow,  or  a  dished  or  cupped  striking  plate  may  be 
substituted  for  the  flat  plate.  A  better  arrangement  is  adopted 
for  some  motces  of  steam-hammers.  The  Warrington  hammer 


FIG.   iia. — Casgrain's  Pile  Cap. 


ART.  ii  RINGS,    CAPS,   AND   FOLLOWERS  31 

substitutes  for  its  ordinary  base  what  is  known  as  the  McDer- 
mid  patent  base  in  which  a  recess  is  provided  for  a  thick  steel 
plate  inserted  through  a  slot  in  the  side,  covered  by  a  door. 
The  plate  is  held  in  place  by  the  base  and  thus  avoids  the  danger 
to  the  crew  which  occurs  with  the  separate  flat  or  dished  plate. 
The  Goubert  and  the  McKiernan-Terry  steam-hammers  are 
provided  with  an  anvil  block  in  the  base  and  which  rests  on 
the  pile. 

When  a  pile  has  to  be  driven  below  the  leads,  or  below  the 
ground  or  water  surface,  a  follower  is  generally  employed.  A 
follower  is  a  member  interposed  between  the  hammer  and  a 
pile  to  transmit  blows  to  the  latter  when  below  the  foot  of  the 
leads.  In  its  simplest  form  a  follower  may  consist  of  a  short 
pile  or  stick  of  white  oak  of  the  requisite  length  and  diameter. 
To  keep  its  lower  end  in  position  on  the  pile  a  follower  band 
may  be  used  which  is  flared  both  upward  and  downward,  but 
it  is  better  to  use  a  follower  cap.  This  is  a  cylindrical  casting 
with  a  horizontal  diaphragm  at  the  middle,  which  is  bolted  to 
the  lower  end  of  the  timber  follower,  and  fits  over  the  head  of 
the  pile.  The  upper  end  of  the  follower  is  held  in  position  by 
the  recessed  base  of  the  steam-hammer  or  by  a  pile  cap  if  a 
drop-hammer  is  in  use. 

A  better  kind  of  follower  consists  of  an  extra  strong  pipe 
cast  into  the  base,  so  as  to  avoid  the  objections  to  the  use  of 
bolts.  A  stick  of  turned  hard  wood  is  driven  in  to  the  pipe.  An 
iron  band  is  shrunk  on  the  pipe  so  as  to  project  beyond  the  top 
into  which  is  fitted  a  hooped  oak  driving  block  that  may  be 
replaced  when  worn  out.  Patented  followers  are  also  used,  to 
which  pipes  are  attached  by  which  steam  or  air  may  be  intro- 
duced on  top  of  the  pile  to  release  the  follower  when  such  aid  is 
needed  in  certain  soils.  When  followers  are  used  to  drive  piles 
through  a  considerable  depth  of  water  the  base  of  the  follower 
should  engage  extension  leads  so  as  to  hold  and  guide  the  head 
of  the  pile  properly.  In  deep  water  with  a  swift  current  it  may 
not  be  possible  to  handle  the  follower  effectively.  In  such  cases 
long  piles  are  driven  while  their  heads  remain  above  the  sur- 
face; afterward  they  are  cut  off  at  the  proper  ele 


32  TIMBER   PILES   AND   DRIVERS  CHAP.  I 

The  use  of  a  follower  generally  absorbs  a  considerable  per- 
centage of  the  energy  of  the  hammer,  frequently  amounting  to 
50  percent.  The  loss  is  greater  when  the  lower  end  of  the 
follower  is  not  guided  by  the  leads  and  the  pile  is  set  into  unu- 
sual vibration.  The  following  record  by  J.  E.  CRAWFORD 
shows,  however,  that  under  proper  conditions  there  may  be  no 
appreciable  loss  in  the  effect  of  the  blow.  The  pile  sank  of  its 
own  weight  6  feet  then  the  hammer  with  its  housing- weighing 
6000  pounds  was  put  on  it,  and  it  sank  5  feet  further.  The 
number  of  blows  for  each  succeeding  foot  of  penetration  were 
9,  5,  13,  20,  14,  16,  17,  15,  3°i  40,  47>  65>  45>  26,  22,  33,  60,  55, 
and  55.  Then  the  follower  was  put  on  and  the  number  of 
blows  required  by  foot  were  55,  75,  56,  60.  73,  90,  113,  115, 
and  102  blows  for  the  last  7  inches,  giving  the  pile  a  pene- 
tration of  39  feet  7  inches. 

ART.  12.     POINTS,  SHOES,  AND  SPLICES 

The  foot  of  a  timber  pile  should  always  be  cut  off  perpen- 
dicular to  its  axis,  since  it  facilitates  driving  it  true  to  line  or 
position.  In  soft  and  silty  ground  or  where  the  driving  is  easy, 
it  is  not  necessary  to  sharpen  or  .point  the  pile.  If  a  pile 
penetrates  soft  material  and  rests  upon  a  hard  stratum,  thus 
acting  as  a  column,  the  unpointed  foot  has  the  additional  ad- 
vantage of  providing  a  larger  bearing  area.  The  blunt  end 
on  striking  a  root  or  any  small  obstruction  will  generally  break 
the  obstruction  without  deflecting  the  pile. 

In  driving  a  pile  with  a  blunt  end  a  cone  of  compressed 
earth  forms  under  it  and  acts  in  most  respects  as  if  the  pile 
were  pointed.  It  is  frequently  claimed  that  even  in  driving 
through  hard  material  a  pile  will  keep  more  nearly  to  the 
required  position  than  if  it  is  pointed.  This  implies  that  the 
cone  of  earth  is  more  likely  to  have  the  form  of  a  fairly  good 
cone  or  pyramid  than  the  wooden  point  made  by  sharpening  the 
pile.  Such  a  contention  can  hardly  be  maintained  if  the  point- 
ing is  properly  done.  When  coarse  gravel  or  boulders  are  en- 
countered which  destroy  the  cone  of  compact  earth,  crush  the 


ART.  12 


POINTS,    SHOES,   AND    SPLICES 


33 


fibers  of  the  timber  and  wedge  them  apart,  it  is  desirable  to 
reduce  the  area  of  the  foot  by  pointing.  In  general,  when  the 
ground  is  at  least  moderately  compressible  and  the  driving  is 
not  hard  the  foot  of  the  pile  may  be  left  unpointed. 

When  the  driving  is  hard  for  most  of  the  penetration,  as  in 
stiff  clay  or  in  material  that  is  but  slightly  compressible  and 
hence  must  be  displaced,  it  is  advisable  to  point  the  pile  that 
it  may  separate  the  material  at  the  foot  like  a  wedge.  In 


FIGS.   1 2a,  b,  and  c. — Shoes  for  Timber  Piles. 

pointing  a  pile  it  is  preferably  sharpened  to  the  form  of  a  trun- 
cated pyramid,  the  end  being  from  4  to  6  inches  square. 
If  the  end  is  too  small  the  fibers  lack  the  necessary  strength 
to  resist  brooming.  The  length  of  the  point  may  be  from  one 
and  a  half  to  twice  the  diameter  of  the  foot.  Another  advan- 
tage of  pointing  is  to  increase  the  rate  of  penetration,  or  to 
reduce  the  energy  required.  In  compact  material  the  bearing 
power  of  a  pile  is  practically  the  same  with  or  without  the  point. 
Experience  has  also  shown  that  piles  with  pointed  ends  may  be 
successfully  driven  through  old  timber  cribwork  while  attempt- 
ing to  drive  them  with  blunt  ends  resulted  in  broomed  tips, 
split  and  broomed  heads. 
3 


34 


TIMBER   PILES    AND   DRIVERS 


CHAP.  I 


Sometimes  the  timber  point  is  replaced  or  protected  by  a 
metal  shoe.  Fig.  1 20,  shows  an  undesirable  form  which  tends 
to  split  the  pile  when  the  side  of  the  shoe  strikes  an  obstruction. 
Figs.  i2b,  c,  and  /  illustrate  the  best  forms,  since  the  timber  has 
a  square  bearing  on  the  upper  flat  surface  of  the  shoe  and  the 
sides  of  the  socket  or  the  straps  permit  such  a  firm  fastening 
as  to  make  the  shoe  act  like  an  in- 
tegral part  of  the  pile.  Those  in 
Figs.  i2d  and  e  are  not  quite  so  effec- 
tive unless  a  close  fit  is  secured  in 
the  socket  at  an  increased  labor  cost. 
Shoes  are  used  by  some  engineers 
when  piles  are  driven  into  material 
containing  boulders,  rip  rap,  coarse 


faf/>  shoe  has  3ho/es. 
I  °for  boat  spikes. 

FIGS.   i2d,  e,  and  /. — Shoes  for  Timber  Piles. 

gravel,  shale,  slate,  hardpan,  buried  timber,  very  hard  clay,  and 
coral  rock.  Another  use  is  to  penetrate  a  thin  hard  stratum 
(2  feet  or  less)  which  overlies  a  softer  one.  They  are  also  at- 
tached to  piles  for  bridge  falsework  in  order  to  gain  a  foothold 
on  rock  bottom.  In  one  case  it  was  thus  possible  to  secure 
sufficient  penetration  to  hold  the  piles  against  a  2o-foot  rise  in 
the  river  and  a  swift  current. 

On  the  Key  West  Extension  of  the  Florida  East  Coast  Rail- 
way where  numerous  pile  foundations  are  built  on  coral  rock 
containing  pockets  of  different  sizes,  a  hole  was  made  by  driving 
a  steel  punch  with  the  pile-hammer  and  then  driving  in  the 
timber  pile  with  a  few  light  blows.  In  order  to  permit  the 


ART.  12 


POINTS,    SHOES,    AND    SPLICES 


35 


punch  to  be  readily  withdrawn,  it  was  provided  with  a  foot 
slightly  larger  in  diameter  than  its  body. 

Some  engineers  and  contractors  condemn  the  use  of  shoes 
unqualifiedly  because  of  their  unsatisfactory  experience,  but 
in  many  cases  such  experience 
is  probably  due  to  employing 
shoes  which  were  improperly 
designed  or  constructed,  while 
in  others  the  piles  should  have 
been  omitted  since  the  ground 
was  hard  enough  to  support 
the  substructure  directly. 

It  is  occasionally  necessary 
to  use  longer  piles  than  can  be 
obtained  in  single  sticks.  It 
becomes  necessary  therefore 
to  splice  two  piles  together  end 
to  end.  For  this  purpose  a 
fish-plate  joint  is  usually  the  ; 
best  since  it  provides  lateral 
resistance.  Either  four  or  six 
timber  fish  plates  may  be  used 
as  illustrated  in  Figs.  i2g  and 
h.  For  the  falsework  to  erect 
the  Poughkeepsie  bridge  55- 


I 


FIGS.  i2g  and  h. — Fish-plate  Splices  for 
Timber  Piles. 


foot  piles  were  spliced  to  75- 
foot  piles  by  means  of  fish 
plates  20  feet  long,  eight  fish 
plates  4  by  5  inches  in  section 
being  fastened  to  the  piles  with 

J-inch  wr ought-iron  spikes  8  inches  long.  The  water  was  55 
feet  deep.  Wrought-iron  fish  plates  may  be  employed  instead 
of  wooden  ones  and  thus  reduce  the  sectional  area  at  the  joint. 
Another  method  is  to  use  a  metal  sleeve  consisting  of  a  piece 
of  heavy  pipe  as  indicated  in  Fig.  122.  Half-lap  joints  fastened 
either  with  bolts,  bands,  or  wire  wrapping  are  often  used  but 
they  are  deficient  in  lateral  strength  and  stiffness. 


TIMBER   PILES   AND   DRIVERS 


CHAP.  I 


In  rebuilding  the  fender  piers  of  the  Thames  River  bridge 
in  1902,  400  piles  were  driven  formed  by  splicing  spruce  piles 
35  to  40  feet  long  to  creosoted  yellow  pine  piles  from  50  to 
65  feet  long.  The  water  was  50  feet  or  less  in  depth,  so  that 
the  spruce  piles  are  below  the  bottom  of  the 
river  and  hence  free  from  the  attacks  of  the 
teredo. 

Pile  splices  may  also  be  required  where 
piles  have  to  be  driven  in  sections  on  account 
of  limited  clearance  under  a  bridge.  Piles  in 
three  sections  have  thus  been  placed  with 
pile-drivers  having  short  leads.  The  sections 
were  joined  together  with  iron  sleeves,  the 
piles  being  found  satisfactory  under  test  loads. 
In  swampy  places  one  pile  is  sometimes  driven 
on  top  of  another  with  only  a  dowel  connecting 
the  two.  Such  a  joint  affords  practically  no 
lateral  stiffness  and  the  upper  section  is  liable 
to  bounce  off  while 'driving  unless  the  dowel 
is  very  long. 

In  pile  trestles  where  the  upper  portions  of 
long  piles  are  decayed  repairs  may  be  made  by  cutting  out 
the  decayed  section  and  inserting  new  timbers.  In  one  case 
four  steel  angles  were  used  as  fish  plates  for  each  pile.  They 
were  well  fastened  with  spikes,  and  each  end  of  the  joint  was 
wrapped  with  a  band  of  heavy  wire,  while  spiral  wrapping 
extended  between  them.  A  shell  of  concrete  was  then  cast 
around  the  joint  to  protect  the  metal.  The  repairs  cost  about 
15  percent  of  the  cost  of  the  piles  in  place. 


FIG.  12*. — Tubu- 
lar Splice  for  Tim- 
ber Pile. 


CHAPTER  II 
DRIVING  TIMBER  PILES 

ART.  13.    OBSERVATIONS  IN  PRACTICE 

As  a  general  rule  a  heavy  hammer  with  a  low  fall  secures 
greater  penetration  with  less  expenditure  of  power  than  a 
light  one  with  a  high  fall;  it  is  also  less  injurious  to  the  equip- 
ment. More  blows  can  be  given  in  the  same  time  with  a  low 
fall  and  hence  less  time  is  given  between  blows  for  the  ground 
to  compact  itself  around  the  pile.  In  quicksand  it  is  especially 
necessary  to  have  the  blows  follow  each  other  as  rapidly  as 
the  operation  of  the  hammer  permits.  In  silt  the  rapidity  of 
blows  need  not  be  quite  so  great  as  for  quicksand. 

When  a  pile  sinks  at  a  uniform  rate  it  is  less  apt  to  jam, 
buckle,  or  split  than  when  driven  with  heavier  blows  and  with 
marked  intervals  of  time  between  them.  This  statement  is 
confirmed  by  observations  in  putting  down  steel  sounding 
rods  by  hand.  For  example,  through  soft  gravel  mixed  with 
quicksand,  one  man  may  be  able  to  push  a  rod  down  5  or  6 
feet,  and  if  quick  enough  may  pull  the  rod  up  again  with  the 
same  expenditure  of  power.  If,  however,  the  rod  is  allowed 
to  rest  no  longer  than  15  seconds  the  sand  packs  against  it 
so  that  two  men  are  scarcely  able  to  pull  it  up.  A  pile  which 
is  left  standing  for  a  few  minutes  in  some  kinds  of  sand  may  be 
packed  so  hard  as  to  resist  further  penetration,  or  at  least  to 
require  a  much  larger  impact  to  start  it  again. 

A  very  slight  bounce  of  a  drop-hammer  occurs  at  every  blow 
under  good  conditions  for  driving,  but  decided  bouncing  of  the 
hammer  may  occur  when  the  penetration  ceases,  or  when  the 
hammer  is  too  light,  or  the  fall  too  great,  or  both;  or  when  the 
head  of  the  pile  is  crushed  or  .broomed  so  as  to  cushion  the 
blow. 

37 


38  DRIVING   TIMBER   PILES  CHAP.  II 

In  certain  kinds  of  soil  a  pile  may  sink  some  distance  and  then 
refuse  to  go  further,  but  will  resume  penetration  when  driven 
after  an  interval  of  rest;  or  it  may  refuse  to  sink  under  a  heavy 
hammer  and  yield  under  the  more  rapid  blows  of  a  lighter  one. 
The  driving  of  one  pile  may  cause  adjacent  piles  to  rise,  and  in 
soft  ground  or  mud  often  causes  an  adjacent  pile  previously 
driven  to  move  away  slightly. 

The  great  variety  of  experiences  which  may  occur  on  a  simple 
work  of  construction  may  be  illustrated  by  those  encountered 
in  driving  piles  for  the  Odgen-Lucien  Cut-off  of  the  Central 
Pacific  Railway.  The  nature  of  the  bottom  of  Great  Salt 
Lake  was  found  to  be  so  variable  that  at  times  a  blow  of  the 
hammer  drove  a  pile  only  i  or  2  inches,  and  at  other  times 
i  or  2  feet;  or  a  pile  seemed  to  strike  a  hard  stratum  and 
refused  to  sink  farther  under  many  blows,  but  after  being 
forced  through,  the  pile  sank  as  much  as  2  or  3  feet  per  blow. 
Frequently  a  pile  with  a  penetration  of  30  to  50  feet  would 
suddenly  rise  2  or  3  feet  during  a  short  delay  of  the  hammer.  At 
the  end  of  the  temporary  trestle,  to  be  later  replaced  by  a 
rock  fill,  a  new  difficulty  was  encountered.  The  first  pile  26 
feet  long  was  driven  out  of  sight  by  a  single  blow,  and  when 
another  pile  28  feet  long  was  placed  on  top  of  it,  the  next 
blow  of  the  hammer  sent  both  out  of  sight.  The  formation 
was  found  to  be  a  deep  mud  deposit  due  to  the  Bear  River.  As 
the  mud  was  50  feet  deep,  two  40-foot  piles  were  driven  on  top 
of  each  other.  The  trestle  supported  by  these  spliced  piles 
supported  the  trains  until  the  rock  fill  was  completed  and 
settled. 

In  certain  kinds  of  clay  the  lateral  spring  of  a  pile  under  the 
hammer  blows  makes  a  hole  slightly  larger  than  the  diameter 
of  the  pile,  allowing  surface  water  to  find  its  way  to  the  foot  of 
the  pile  thus  reducing  both  the  skin  friction  and  the  bearing 
power  of  the  clay  under  the  foot  of  the  pile.  This  action  ex- 
plains why  cases  have  been  observed  where  piles  settled  under 
moving  trains  after  a  rain  although  the  resistance  of  the  pile 
when  driven  was  considered  satisfactory.  The  treatment  of 
such  conditions  is  indicated  in  Art.  16. 


ART.  13  OBSERVATIONS  IN  PRACTICE  39 

The  principle  involved  may  be  advantageously  applied  in 
some  cases  to  reduce  the  resistance  in  pile  driving  when  there  is 
no  available  water-jet  equipment.  For  example,  by  discharg- 
ing water  on  the  surface  of  the  ground  at  the  pile  with  an  ordi- 
nary garden  hose,  without  a  nozzle,  the  number  of  blows  by  a 
steam-hammer  was  reduced  from  296  to  164  for  a  45-foot  pile 
in  a  Chicago  building  foundation. 

One  engineer  declared  in  a  discussion  on  this  subject  that 
sometimes  hardly  a  day  passed  but  someone  rushed  into  the 
office  to  state  that  in  a  certain  place  the  piles  were  being  driven 
too  deep;  that  they  had  gone  through  a  hard  stratum  into  a 
weaker  one,  forgetting  that  in  ground  where  its  supporting 
power  depends  mainly  upon  skin  friction  the  total  penetration 
must  be  large. 

A  frequent  cause  of  small  penetrations  per  blow  is  the 
crookedness  of  a  pile  which  produces  a  lateral  spring  under  the 
hammer  blow,  and  thus  dissipates  some  of  the  energy.  Occa- 
sionally it  is  due  to  the  head  of  the  pile  being  cut  off  improperly 
so  that  the  hammer  strikes  on  one  side  only.  Perhaps  the 
most  common  cause  is  due  to  setting  the  pile  out  of  plumb  in 
the  leads,  on  account  of  undue  haste  or  carelessness.  It  is 
equally  as  important  to  keep  the  leads  plumb  by  leveling  up  the 
tracks  on  which  the  pile-driver  moves. 

Under- ground  conditions  sometimes  force  a  pile  out  of  line 
in  spite  of  ordinary  efforts  to  control  its  movements  in  the 
leads.  A  block  and  tackle  or  a  jack  screw  may  be  required 
to  force  it  back. 

If  it  is  desired  to  compact  the  ground  in  a  given  area  uni- 
formly, it  is  best  to  begin  driving  piles  at  the  center  and  work 
outward  to  the  perimeter.  If  the  order  of  procedure  is  reversed, 
it  becomes  more  and  more  difficult  to  drive  the  piles  toward 
the  middle  to  secure  the  same  penetration  and  usually  the 
adjacent  outer  piles  will  be  forced  to  rise  more  or  less. 

It  is  often  instructive  to  notice  the  effect  on  piles  in  place 
when  additional  ones  are  driven  near-by.  One  may  observe 
piles  which  were  cut  off  to  grade  rising  from  2  to  3  inches  when 
adjacent  piles  are  driven,  showing  that  the  ground  between 


40  DRIVING   TIMBER  PILES  CHAP.  II 

the  piles  is  thoroughly  compacted  and  that  its  vertical  motion 
indicates  the  line  of  least  resistance.  If  time  permits  they  may 
be  given  some  extra  blows  to  settle  them,  or  they  may  be  cut 
off  again  to  grade  since  the  phenomenon  shows  that  the  full 
supporting  power  which  the  nature  of  the  ground  permits  is 
being  applied  to  the  pile. 

On  foundation  work  for  the  Illinois  Central  Passenger  Sta- 
tion at  Chicago  a  group  of  eight  piles  had  been  driven,  sawed  off 
to  a  uniform  height,  and  wales  drift-bolted  to  them.  Upon 
driving  a  group  of  16  piles  15  feet  away,  the  piles  in  the  former 
group  rose  4  inches  next  to  the  driver  and  i  inch  on  the 
opposite  side.  In  a  group  of  72  piles  observations  were  taken 
daily  on  the  head  of  the  first  pile  while  the  rest  were  being 
driven.  The  pile  sank  \  inch  during  the  first  two  days,  then 
rose  steadily  until  50  piles  were  in  place  when  it  was  3  inches 
above  the  original  elevation,  the  greatest  rise  in  one  day  being  f 
inch.  The  pile  was  55  feet  long,  and  had  a  total  penetra- 
tion of  45  feet. 

The  distance  to  which  vibration  was  felt  at  the  same  site 
varied  with  the  height  of  fall  of  the  hammer,  the  nature  of 
the  ground  and  the  spacing  of  the  piles.  The  vibration  was 
easily  felt  at  a  distance  of  400  feet  and  was  quite  marked  at 
75  feet.  In  doing  instrumental  work  it  was  sometimes  observed 
that  the  vibration  within  25  feet  of  the  pile-driver  was  less 
severe  than  at  several  times  that  distance. 


ART.  14.     DRIVING  PILES  BUTT  DOWN 

It  is  the  general  practice  to  drive  piles  with  the  tip  downward. 
Occasionally,  however,  special  conditions  make  it  advisable  to 
drive  them  with  the  butt  downward.  It  has  been  found  diffi- 
cult at  times  to  keep  a  pile  down  after  being  struck  by  the 
hammer,  the  pile  beginning  at  once  to  rise,  lifting  the  hammer 
with  it;  and  upon  raising  the  hammer  the  pile  may  shoot  up- 
ward 5  feet  or  more,  or  the  pile  may  exhibit  this  tendency 
but  slightly  when  driven,  but  the  following  morning  will  stand 
with  its  head  a  number  of  feet  higher  than  before.  This  be- 


ART.  15  DRIVING  BATTER  PILES  41 

havior  is  ascribed  to  a  substratum  of  quicksand,  and  the 
difficulty  is  usually  overcome  by  driving  the  pile  'butt  down.' 

Another  condition  occurs  when  piles  are  driven  through 
very  soft  ground  and  the  load  has  nearly  all  to  be  borne  by 
the  foot.  The  substratum  may  require  the  larger  bearing  area 
afforded  by  the  butt  of  the  pile  to  carry  the  load.  Some  engi- 
neers recommend  that  tall  pile  trestles  which  are  to  be  filled 
should  have  the  piles  driven  butt  down,  thus  leaving  no  hollows 
to  cause  trouble  as  the  embankment  settles.  The  bracing  can 
be  removed  as  the  filling  rises.  In  hard  material  the  butt 
may  have  to  be  pointed  to  a  smaller  diameter  to  facilitate  pene- 
tration. Great  care  must  be  exercised  in  driving  on  account  of 
the  smaller  area  of  the  tip,  which  receives  the  blow,  the  smaller 
percentage  of  heartwood  in  that  area  and  the  weaker  fibers  of 
the  wood  which  grows  in  the  upper  part  of  a  tree  trunk. 

In  some  cofferdam  construction  on  the  Ohio  river  where  it 
was  necessary  to  drive  about  600  oak  guide  piles  into  hard 
gravel  it  was  found  that  the  best  way  to  secure  adequate  pene- 
tration was  to  drive  them  with  the  butts  down.  In  this  manner 
the  resistance  encountered  due  to  the  wedge  action  of  piles  as 
usually  driven  was  avoided,  and  the  useful  effect  of  the  blow 
was  all  transmitted  to  the  foot  of  the  pile. 

An  interesting  example  relates  to  piles  driven  4  to  6  feet 
apart  both  ways  in  the  embankment  of  the  Yazoo  canal  near 
Vicksburg,  Miss.,  to  stop  the  bank  from  sliding  on  the  adja- 
cent railroad  track  during  the  low- water  stage  of  the  river. 
By  driving  the  piles  butt  down  advantage  was  taken  of  the 
larger  cross-section  at  the  lower  elevation  where  the  bending 
moment  was  a  maximum.  Pile  trestles  have  resisted  the 
pressure  of  ice  going  out  by  having  extra  flexural  strength 
due  to  the  piles  being  driven  butt  down.  When  piles  have  to  be 
driven  into  sand  with  their  butts  down  the  water-jet  should 
be  employed  (Art.  16). 

ART.  15.     DRIVING  BATTER  PILES 

A  batter  pile  is  a  pile  driven  at  an  inclination  to  resist  forces 
which  are  not  vertical.  It  is  sometimes  called  a  spur  pile. 


42  DRIVING    TIMBER   PILES  CHAP.  II 

When  a  pile-driver  is  designed  to  drive  batter  piles  as  well  as 
the  ordinary  vertical  piles,  its  leads  are  suspended  from  a 
horizontal  pin  to  permit  them  to  be  swung  laterally  like  a 
pendulum.  Hence  they  are  known  as  swinging  leads  and 
sometimes  as  pendulum  leads.  The  pivot  is  attached  to  the 
top  of  a  tower,  the  front  timbers  of  which  are  inclined  laterally 
to  provide  the  requisite  transverse  bracing.  Fig.  150  shows 
batter  piles  being  driven  in  the  trestle  approach  of  the  Dum- 
barton bridge  across  San  Francisco  Bay.  Although  this  illus- 
tration is  that  of  a  track  driver,  the  arrangement  of  swinging 
leads  shown  is  the  same  as  for  ordinary  land  drivers  or  for 
floating  pile-drivers. 

Occasionally  drivers  are  arranged  to  drive  batter  piles  by 
having  a  removable  section  at  the  bottom  of  the  back  stays,  so 
that  the  tower  revolves  backward  about  hinges  located  near 
the  foot  of  the  leads.  Another  scheme  consists  in  taking  a 
separate  set  of  leads  and  temporarily  bracing  them  to  the  tower 
of  a  pile-driver.  In  this  manner,  batter  piles  60  to  70  feet 
long  were  driven  for  car  dump  foundations  at  the  Erie  Rail- 
road Dock  at  Cleveland,  the  piles  sloping  downward  toward 
'the  driver. 

An  interesting  form  of  pile-driver  was  used  in  1904  to  drive 
piles  for  a  permanent  extension  on  the  Ogden-Lucien  Cut-off 
which  crosses  the  western  arm  of  Great  Salt  Lake.  It  was  de- 
signed to  operate  from  a  low  falsework  built  alongside,  the 
tower  overhanging  the  track.  The  leads  were  arranged  to 
swing  forward  below  to  drive  the  piles  and  whenever  a  train 
came  along  they  could  be  swung  back  between  the  timbers 
in  the  tower  corresponding  to  fixed  leads.  The  king  pin  support- 
ing the  leads  was  placed  directly  over  the  center  of  the  track, 
so  that  the  leads  had  their  correct  position  and  direction  to 
drive  the  respective  piles  of  each  bent  when  the  proper  pins 
were  inserted  in  the  struts  holding  the  leads.  Two  sets  of 
rollers  were  set  under  the  sills  of  the  driver,  the  lower  set  to 
allow  the  driver  on  the  falsework  to  move  parallel  to  the 
trestles  and  the  upper  to  move  at  right  angles  to  it,  to  place 
the  driver  in  the  clear  of  passing  trains. 


FIG.  150. — Driving  Batter  Piles  on  the  Trestle  Approach  to  the  Central  California 
Railway  Bridge  over  San  Francisco  Bay  at  Dumbarton  Point,  August,  14,  1907. 

(Facing  p.  42.) 


FIG.  1 8a.—  Examples  of  Overdriven  Piles  Exposed  by  Subsequent  Excavation. 


ART.  1 6  USE   OF   THE   WATER- JET  43 

Batter  piles  are  used  under  arch  abutments  to  resist  the 
horizontal  component  of  the  reaction,  and  sometimes  several 
are  employed  under  each  side  of  piers  for  simple  truss  or  girder 
spans  when  the  weight  of  the  pier  is  not  sufficient  to  provide 
adequately  for  the  effect  of  traction.  Quay  walls  are  provided 
either  with  batter  piles  or  with  rods  to  anchor  piles,  or  both. 
Many  accidents  to  such  structures  have  occurred  because  of 
a  failure  to  provide  batter  piles  to  relieve  the  vertical  piles  from 
flexural  stresses.  Vertical  piles  in  permanent  structures  should 
be  protected  against  the  action  of  lateral  forces  whenever  possi- 
ble either  by  sway  bracing  or  by  batter  piles.  See  Fig.  13  5<; 
for  an  illustration  of  the  use  of  batter  piles  in  the  foundation 
of  a  bridge  pier. 

ART.  1 6.     USE  OF  THE  WATER- JET 

A  method  of  placing  a  pile  in  position,  which  differs  radically 
from  that  of  driving  it  with  a  hammer,  consists  in  displacing 
the  material  by  means  of  one  or  more  jets  which  discharge 
water  under  pressure  at  or  near  the  foot  of  the  pile.  As  the 
water  comes  up  around  the  pile  carrying  with  it  some  of  the 
material  it  also  diminishes  the  frictional  resistance  of  the 
pile.  In  some  kinds  of  earth  the  hammer  is  merely  placed  on 
top  of  the  pile  to  increase  the  pressure  by  its  weight,  while 
in  other  cases  the  hammer  is  operated  with  a  restricted  fall  to 
secure  a  greater  rate  of  penetration. 

In  soft  ground  one  jet  may  answer  the  purpose,  but  in  most 
cases  two  jets,  used  on  opposite  sides  of  the  pile,  give  better 
results.  As  the  pile  tends  to  move  toward  the  side  where  the 
jet  is  operated,  the  use  of  two  jets  usually  enables  a  pile  to  be 
placed  more  accurately  in  position.  Sometimes  a  third  jet  is 
employed,  discharging  at  a  higher  elevation  than  the  others, 
if  difficulty  is  experienced  in  keeping  the  ground  from  packing 
against  the  sides  of  the  pile. 

The  water  has  a  puddling  action  upon  the  adjacent  earth 
and  after  the  jet  is  removed  the  earth  packs  closely  around 
the  surface  of  the  pile,  thus  securing  a  greater  skin  friction 


44  DRIVING   TIMBER  PILES  CHAP.  II 

than  if  the  pile  is  driven  by  means  of  the  hammer  alone.  In 
order  to  secure  better  bearing  at  the  foot,  it  is  customary 
to  shut  off  the  water  just  before  the  pile  reaches  its  intended 
total  penetration,  and  to  complete  the  driving  by  a  few  blows 
of  the  hammer.  This  procedure  presses  the  pile  firmly  into 
the  softened  earth  and  tends  to  avoid  any  arching  action  of 
the  earth  that  might  prevent  the  material  from  filling  every 
cavity  when  it  settles  into  place. 

The  water-jet  may  be  used  advantageously  in  any  material 
that  will  settle  around  the  pile  after  the  flow  of  water  ceases. 
The  best  results  are  obtained  in  pure  ocean  or  river  sand. 
In  this  material  the  simplest  form  of  jet  may  be  used,  only  a 
moderate  pressure  is  required,  a  single  jet  will  generally  answer, 
the  time  of  sinking  is  very  short,  and  the  sand  packs  quickly 
after  the  water  is  shut  off,  while  no  blows  of  the  hammer  are 
needed  except  for  the  purpose  stated  in  the  preceding  para- 
graph. It  is  fortunate  that  this  is  the  case  for  pure  sand 
offers  very  high  resistance  to  a  pile  when  driven  with  the  ham- 
mer alone,  especially  with  a  drop-hammer.  Even  in  quicksand 
this  is  frequently  found  to  be  true.  With  the  jet  a  pile  may  be 
sunk  in  sand  without  danger  of  injury,  while  it  is  difficult  to 
avoid  injuring  piles  when  driven  into  sand  without  the  aid  of 
the  jet;  more  time  and  a  larger  expenditure  of  energy  are  also 
required. 

Piles  have  been  driven  with  the  aid  of  the  water-jet  process 
in  mixtures  of  sand  and  silt  or  gravel,  if  the  latter  is  not  too 
coarse;  in  loam,  clay,  marl,  and  even  'gumbo'  in  pockets,  al- 
though a  special  nozzle  is  required  for  the  material  named  last. 
Some  of  the  most  experienced  engineers  ,in  the  use  of  the  jet 
have  driven  piles  with  its  aid  in  "sand  and  clay  and  the  hardest 
kind  of  bottom,"  and  in  "almost  any  material  except  hard-pan 
and  rock."  In  hard  ground  the  jet  process  may  be  used  advan- 
tageously in  case  sufficient  volume  and  pressure  of  water  be 
provided.  In  clay  it  may  be  economical  to  bore  several  holes 
in  the  earth  before  driving  the  pile,  thus  securing  the  accurate 
location  of  the  pile  and  its  lubrication  while  being  driven. 
Where  the  material  is  of  such  a  porous  character  that  the 


ART.  16  USE   OF   THE   WATER- JET  45 

water  from  the  jets  may  be  dissipated  and  fail  to  come  up  in 
the  immediate  vicinity  of  the  pile,  the  utility  of  the  jet  process 
is  uncertain  except  for  a  part  of  the  penetration.  In  mixtures 
with  gravel  or  coarse  material  the  water  will  often  wash  out 
the  sand  and  finer  material  leaving  the  stones  in  the  hole  to 
interfere  with  the  penetration  of  the  pile.  This  action  may 
often  be  remedied,  however,  by  increasing  the  volume  and 
pressure  of  the  water. 

In  driving  in  sand  the  jet  should  be  hung  on  a  rope  passing 
over  a  pulley  in  the  driver  so  that  it  may  be  kept  moving  up 
and  down  with  its  point  near  the  point  of  the  pile.  If  this 
is  not  done  the  pipe  is  likely  to  'freeze'  fast  and  cannot  be 
moved.  After  the  pile  reaches  a  depth  of  10  or  15  feet  the 
water  will  sometimes  fail  to  come  up  around  it,  breaking  out 
on  the  surface  at  a  considerable  distance,  perhaps  around  a  pile 
driven  previously.  When  this  occurs  it  indicates  that  the  jet 
has  not  been  kept  moving  sufficiently,  or  an  auxiliary  jet  may 
be  needed  discharging  at  some  intermediate  depth.  In  any 
case  the  jet  should  be  withdrawn  at  once  and  immediately  put 
down  again,  thus  usually  reestablishing  the  flow  of  water  along 
the  pile.  Where  piles  are  sunk  20  feet  or  more  into  sand  it  is 
advisable  to  have  two  jets.  One  is  to  be  kept  moving  with  its 
nozzle  slightly  ahead  of  the  pile,  while  the  other  is  slowly 
raised  and  lowered  between  the  foot  of  the  pile  and  the  surface 
to  maintain  the  flow  along  the  pile.  On  the  other  hand,  when 
the  material  is  soft  and  readily  compressible  as  in  silt,  or  in  fine 
sand  mixed  with  silt  or  a  small  percentage  of  clay,  it  may  not 
be  economical  to  use  a  jet  since  the  pile  may  be  driven  quickly 
without  risk  of  injury  by  means  of  a  steam-hammer. 

The  effectiveness  of  the  water-jet  is  demonstrated  at  times 
during  the  operation  of  sinking  a  pile  when  a  break-down 
occurs,  and  an  attempt  is  made  to  drive  temporarily  without  its 
aid.  So  frequently  will  the  piles  broom  or  split,  or  give  other 
signs  of  injury  before  reaching  the  full  depth  of  penetration, 
as  to  preclude  further  driving.  When  piles  were  first  driven  at 
Atlantic  City  prior  to  1890,  a  contractor  became  bankrupt  by 
attempting  to  drive  piles  in  the  wet  sand  by  means  of  the  ham- 


46  DRIVING  TIMBER  PILES  CHAP.  II 

mer  alone.  A  score  of  years  later  when  the  water-jet  was  gen- 
erally used  in  that  locality  contractors  were  wont  to  consider 
it  as  an  ordinary  performance  to  sink  100  to  120  piles  in  a  half 
day.  This  fact  illustrates  the  saving  in  time  and  money  which 
is  made  possible  by  the  aid  of  the  jet. 

In  Florida  palmetto  piles  are  sometimes  used  since  they  are 
comparatively  free  from  the  ravages  of  the  teredo.  This  wood 
has  a  hard  shell  and  a  soft  interior,  and  cannot  stand  heavy  blows 
with  a  hammer.  Such  piles  may  be  easily  sunk  into  hard  sand 
by  a  water-jet,  the  hammer  resting  on  top  and  occasionally 
tapping  the  pile,  the  fall  being  only  3  to  6  inches.  By  keeping 
the  pile  and  jet  pipes  constantly  moving  the  sand  is  kept  from 
closing  in  on  the  pile  until  it  occupies  its  final  position.  With 
the  aid  of  the  jet,  piles  may  be  sunk  as  readily  with  the  butt 
down  as  with  the  tip  down. 

In  general  the  water-jet  should  not  be  attached  to  the  pile, 
but  handled  separately.  The  nozzle  is  usually  extended  a  small 
distance,  not  exceeding  a  foot,  below  the  foot  of  the  pile,  but 
sometimes  it  is  necessary  to  move  it  up  and  down  to  reduce 
the  frictional  resistance  on  the  pipe,  or  to  change  its  position 
if  a  boulder  is  encountered,  so  as  to  excavate  an  opening  into 
which  the  boulder  may  he  pushed  by  the  p^e.  If  this  is  not 
sufficient  to  displace  an  obstruction  the  pile  may  be  raised  a 
little  and  dropped  with  the  hammer  resting  upon  it.  It  is  not 
desirable  to  bend  the  pipe,  as  is  sometimes  done  just  above 
the  nozzle.  For  depths  not  exceeding  15  to  20  feet  and  when 
the  ground  does  not  consist  of  layers  differing  materially  in 
character,  the  average  rate  of  penetration  is  often  found  to 
be  remarkably  uniform,  independently  of  the  depth. 

At  the  Brooklyn  anchorage  of  the  Manhattan  bridge  2500 
piles  were  driven,  about  40  feet  long  and  14  to  16  inches  in 
diameter  at  the  butt.  Great  difficulty  was  experienced  in 
driving  them  on  account  of  the  numerous  large  and  small 
boulders  encountered  and  a  thin  stratum  of  hard-pan  that  had 
to  be  penetrated.  With  the  hammer  alone  test  piles  could  be 
driven  only  8  to  10  feet,  but  with  the  aid  of  a  powerful  hydraulic 
jet  they  could  be  driven  to  a  depth  of  40  feet.  When  a  boulder 


ART.  16  USE   OF   THE   WATER-JET  47 

was  encountered  the  jet  was  worked  around  its  edges  until  it 
was  moved  aside,  or  until  it  was  undermined  and  finally  sunk 
to  a  position  below  the  foot  of  the  pile  at  its  desired  elevation. 
The  continued  use  of  the  jet  softened  the  ground  when  it  could 
not  excavate  it  so  that  the  pile  could  be  driven  further  to  its 
final  grade.  In  this  manner  piles  were  driven  where  it  would 
have  been  impossible  to  do  so  without  the  jet.  Boulders  two 
cubic  yards  in  volume  were  sometimes  displaced. 

In  using  the  water-jet,  the  quantity  of  water  should  be 
ample.  In  most  cases  volume  rather  than  velocity  is  necessary. 
The  velocity  must  be  sufficient  to  excavate  the  sand  below 
the  foot  of  the  pile  and  to  make  it  'live'  or  'quick,'  while  the 
volume  is  large  enough  to  force  the  water  to  escape  by 
rising  along  the  sides  of  the  pile  to  bring  the  material  to  the 
surface,  and  at  the  same  time  to  reduce  the  surface  friction, 
if  it  does  not  entirely  eliminate  it.  In  beach  sand,  piles  have 
been  jetted  down  within  18  inches  from  adjacent  piles  without 
disturbing  them,  showing  that  in  this  material  the  movement 
of  the  water  is  confined  to  a  small  radius  horizontally.  In 
cities  the  water-jet  cannot  be  used  as  freely  as  elsewhere  on 
account  of  the  danger  of  settlement  to  adjacent  foundations 
and  injury  to  the  heavy  structures  supported  by  them. 

Where  piles  are  to  be  driven  to  the  uneven  surface  of  an 
underlying  ledge  of  rock  the  proper  length  of  pile  may  be  de- 
termined conveniently  by  running  the  jet  down  to  the  rock 
and  measuring  the  penetrating  length  of  pipe.  The  bearing 
power  of  piles  sunk  by  the  water- jet  process  is  determined  by  test 
blows  of  the  hammer  after  the  material  has  had  time  to  settle 
or  pack  around  the  pile.  In  pure  sand  the  pentration  per  blow 
is  so  small  that  the  bearing  power  of  the  pile  is  limited  either 
by  the  safe  compressive  strength  of  the  wood  of  which  it  is 
composed,  or  by  its'  strength  as  a  column  in  case  the  total  pene- 
tration is  only  a  part  of  its  length. 

The  earliest  authenticated  use  of  the  water-jet  in  sinking 
piles  appears  to  have  been  introduced  on  the  construction  of 
a  wharf  at  Decrow's  Point,  Matagorda  Bay,  Texas,  in  1852, 
and  to  have  arisen  from  a  suggestion  made  by  Lieut.  GEORGE 


48  DRIVING   TIMBER   PILES  CHAP.  II 

B.  McCLELLAN,  Corps  of  Engineers,  U.  S.  A.  The  water  was 
pumped  by  an  ordinary  hand  pump  through  a  rubber  hose  with 
a  gas-pipe  nozzle,  the  nozzle  being  placed  close  to  the  tip  of  the 
pile.  The  historical  development  of  the  water-jet  process  is 
described  at  length  in  an  article  on  The  Water -Jet  as  an  Aid 
to  Engineering  Construction,  by  L.  Y.  SCHERMERHORN,  in  Pro- 
ceedings of  the  Engineer's  Club  of  Philadelphia,  1900,  vol. 
17.  The  use  of  the  water-jet  in  driving  concrete  piles  is  treated 
in  Art.  49. 

ART.   17.    EQUIPMENT  FOR  WATER- JET  PROCESS 

The  water-jet  consists  generally  of  a  straight  pipe  with  a 
nozzle  at  its  end,  connected  by  some  length  of  flexible  hose  to 
the  discharge  pipe  from  the  pump  which  provides  the  water 
under  pressure.  The  suction  pipe  connects  the  pump  with 
the  source  of  water  supply.  The  pump  is  operated  by  steam, 
being  connected  either  with  the  boiler  for  the  pile-driver  or 
with  a  separate  steam  supply.  Sometimes  a  short  piece  of 
curved  pipe  is  coupled  between  the  straight  jet  pipe  and  the 
hose.  The  pipe  can  be  raised  and  lowered  by  a  line  attached 
to  the  top  leading  over  a  snatch  block  to  be  operated  by  hand 
power  on  the  ground,  or  to  a  spool  on  the  hoisting  engine. 

The  diameter  of  the  jet  pipe  is  either  2  or  i\  inches.  The 
discharge  pipe  of  the  pump  is  in  most  cases  4  inches  in  diam- 
eter while  the  diameter  of  the  suction  pipe  is  6  inches.  To 
increase  the  velocity  of  the  water  and  thus  increase  its  power 
to  loosen  the  earth,  the  size  of  the  pipe  is  drawn  down  at  the 
end  to  form  a  nozzle.  The  nozzle  is  usually  circular  in  section 
and  its  diameter  varies  from  f  to  \  inch.  In  a  few  cases  a 
rose-jet  has  been  employed,  the  nozzle  having  one  central 
opening  at  the  end  and  five  openings  around  the  sides  with 
their  axes  inclined  about  45  degrees  to  that  of  the  axes  of  the 
pipe.  (See  Fig.  gib.)  Another  form  of  nozzle  is  made  by 
flattening  the  end  of  the  pipe  until  the  opening  is  reduced  to 
\  inch.  This  nozzle  has  given  better  results  than  a  round  one, 
especially  in  stiff  material,  it  being  rotated  back  and  forth 
about  its  axis. 


ART.  1 8  OVERDRIVING  PILES  49 

The  quantity  of  water  to  be  discharged  varies  from  50  to 
250  gallons  per  minute.  It  must  be  sufficient  to  bring  to  the 
surface  the  material  which  is  next  to  the  pile.  The  pressure 
ranges  from  65  to  200  pounds  per  square  inch  although  the  hose 
and  fittings  are  sometimes  designed  to  resist  a  pressure  of  250 
pounds  per  square  inch.  The  higher  pressures  are  required 
especially  when  gravel  and  boulders  are  encountered.  Recipro- 
cating pumps  are  employed,  either  single  acting  or  double 
acting,  and  sometimes  compounds.  The  error  which  is  most 
frequently  made  is  to  use  pumps  of  insufficient  capacity, 
leading  to  ineffective  work  with  the  jet  and  loss  of  time.  Un- 
satisfactory results  with  the  water-jet  due  to  inadequate  and 
inefficient  equipment  is  doubtless  one  of  the  main  reasons  why 
the  water-jet  process  has  not  come  into  more  extensive  use 
in  pile-driving  practice. 

A  device  has  been  invented  by  which  the  jet  pipe  is  handled 
by  means  of  the  water  pressure,  thus  reducing  hand  labor  to 
a  minimum.  By  turning  a  valve  the  operator  who  guides  the 
pipe  near  the  pile  can  control  the  direction  and  pressure  of  the 
water  so  as  to  raise  or  lower  the  jet  or  to  hold  it  in  any  given 
position.  The  jet  pipe  acts  as  a  plunger  inside  of  a  larger  pipe 
which  acts  as  a  cylinder,  the  latter  being  suspended  from  a 
derrick  pile-driver. 

ART.  18.     OVERDRIVING  PILES 

Examples  of  piles  which  were  injured  by  overdriving  are 
occasionally  exposed  by  subsequent  excavation.  In  Jersey 
City  some  piles  were  driven  into  the  surface  of  a  street  to  sup- 
port temporarily  a  large  water  pipe,  and  afterward  the  street 
had  to  be  excavated  for  the  passage  of  a  railroad.  It  was 
thought  that  the  piles  were  well  driven  and  in  good  condition. 
It  was  discovered  that  about  one-half  of  them  were  ruined  in 
driving,  some  being  broken  off  square  across  and  the  upper 
piece  driven  alongside  the  lower  piece.  One  pile  encountered 
a  large  flat  rock  about  16  feet  below  the  surface,  and  the  fibers 
of  the  tip  were  found  to  have  turned  aside  horizontally  to  a 
distance' of  15  feet. 

4 


50  DRIVING   TIMBER   PILES  CHAP.  II 

In  Brooklyn  before  making  certain  subway  excavations 
timber  piles  had  been  driven  on  the  sides  of  the  street  to  sup- 
port temporary  plank  roadways.  When  they  were  exposed  by 
the  steam  shovel  it  was  seen  that  very  many  of  them  were 
broken,  splintered,  or  sheared.  It  was  known  from  their  be- 
havior during  driving  that  some  of  the  piles  were  overdriven, 
but  the  injuries  proved  to  be  more  numerous  than  had  been 
supposed.  The  piles  were  mostly  spruce  as  yellow  pine  would 
not  stand  the  hard  driving.  The  average  diameter  at  the  butt 
was  12  inches  and  after  a  preliminary  test  20  feet  was  found  to 
be  the  most  satisfactory  length.  A  2ooo-pound  drop-hammer 
was  used  with  a  fall  ordinarily  of  25  feet.  Although  a  water- 
jet  aided  in  driving,  it  was  difficult  to  secure  the  desired  total 
penetration.  The  pile  fractures  had  a  variety  of  forms;  some 
were  splintered  and  broomed,  others  burst  and  were  spread 
out,  while  others  were  sheared  apart,  and  the  upper  end  driven 
past  the  stub. 

In  western  Massachusetts  where  a  new  railroad  passed  under 
an  old  railroad  embankment,  temporary  bents  of  piles  were 
driven  about  22  feet  deep  through  fine  compact  sand.  The 
driving  was  hard  and  no  water-jet  was  employed.  The  ex- 
cavation of  the  bank  showed  over  half  of  the  piles  to  be  seriously 
damaged,  being  split  or  broken  at  distances  exceeding  8  feet 
below  the  surface.  In  most  cases  the  break  was  a  double  shear, 
the  upper  part  acting  as  a  wedge  to  split  the  lower  piece;  some 
failed  by  a  single  inclined  shear,  and  a  few  by  bulging.  Some- 
times bulging  assumes  the  condition  of  collapsing  like  an 
accordion. 

In  1907  while  sinking  a  pneumatic  caisson  for  the  Vancouver 
bridge  over  the  Columbia  River  some  piles  were  removed 
which  had  been  driven  in  1890.  Their  tips  were  found  to  be 
broomed  and  shattered  by  driving  into  the  compact  gravel 
which  they  did  not  penetrate. 

During  excavation  for  a  building  in  New  Orleans  it  was  seen 
that  not  all  the  test  piles  previously  driven  had  pierced  the  sand 
stratum.  Those  with  knotty  ends  had  broken  off  some  dis- 
tance from  the  tip,  and  the  new  tip  thus  formed  reached  the  sand. 


ART.  18  OVERDRIVING  PILES  51 

In  some  instances  two  such  breaks  had  occurred.  One  of  the 
test  piles  had  not  even  penetrated  to  the  depth  of  cut-off  for  the 
foundation  piles  to  be  driven  later.  Some  feet  in  length  above 
the  tip  showed  a  mass  of  fibers,  resembling  worn-out  rope,  of 
about  the  same  shape  and  size  as  a  barrel. 

The  effect  of  continuing  to  drive  temporary  piles  after  the 
tip  reaches  rock  was  clearly  shown  during  excavation  at  a 
tunnel  portal  in  New  York.  Piles  were  furnished  to  the  fore- 
man in  charge  of  the  excavation  somewhat  longer  than  neces- 
sary to  reach  rock  at  the  elevation  indicated  by  the  borings,  and 
he  was  instructed  to  drive  them  to  rock.  The  foreman  reported 
that  he  had  driven  the  piles  as  far  as  possible  without  bringing 
the  butts  below  the  upper  wales  which  they  were  intended  to 
support,  and  that  they  had  not  reached  rock,  insisting  that 
they  had  moved  quite  uniformly  until  he  stopped  driving.  For 
a  number  of  feet  the  lower  ends  of  the  piles  were  badly  shat- 
tered and  broomed  as  revealed  by  the  subsequent  excavation, 
although  the  heads  were  not  broomed  materially. 

A  contracting  engineer  of  large  experience  has  expressed 
his  conclusion  that  more  piles  are  dangerously  injured  by 
improper  driving  than  are  rendered  unsafe  through  insufficient 
driving.  Another  engineer  concludes  that,  in  general,  piles 
are  apt  to  be  overdriven  and  much  of  their  value  lost.  The 
former  believes  that  this  is  due  largely  to  the  use  of  drop- 
hammers  with  excessive  weights  and  undue  heights  of  fall.  He 
reported  a  case  where  ten  successive  piles  in  an  important 
foundation  were  driven  in  hard  material  with  a  3ooo-pound 
drop-hammer  and  a  fall  of  30  feet  and  after  practically  reaching 
'refusal'  suddenly  moved  several  inches  at  the  head.  The 
inspector  in  charge  accounted  for  the  resumption  of  penetration 
by  assuming  that  the  foot  of  the  pile  had  met  and  passed  through 
a  layer  of  hard  material.  The  subsequent  removal  of  these 
piles  showed  that  every  one  had  been  broken  near  mid-length. 
He  also  had  frequent  occasion  in  the  removal  of  timber -pile 
piers  to  examine  the  piles  after  they  were  withdrawn  and  found 
that  when  driven  to  hard  bottom  they  were  generally  either 
broken  at  a  considerable  distance  above  the  foot,  or  else  the 


52  DRIVING  TIMBER  PILES  CHAP.  II 

foot  had  split  and  spread  out  so  as  to  resemble  an  inverted 
mushroom  several  feet  in  diameter.  He  claimed,  moreover, 
that  excessive  driving  results  in  a  degeneration  of  the  fiber 
which  reduces  the  strength  of  the  piles  acting  as  columns  and 
hastens  decay  materially. 

A  contractor,  having  noticed  the  apparently  injurious  effect 
on  piles  due  to  very  heavy  blows,  ordered  experiments  to  be 
made  to  learn  just  what  damage  was  done  and  the  proper 
remedy.  Spruce  and  yellow  pine  piles  40  to  50  feet  long,  1 2  to 
15  inches  at  the  butt  and  6  to  8  inches  at  the  tip  were  driven 
into  a  mixture  of  clay,  sand,  gravel,  and  small  cobble  stones, 
and  which  offered  a  gradually  increasing  resistance  to  penetra- 
tion. A  drop-hammer  weighing  3000  pounds  was  used  with 
the  hoisting  rope  attached.  The  object  was  to  determine  what 
height  of  fall  could  be  safely  adopted  without  impairing  the  in- 
tegrity of  the  pile  either  by  brooming  its  head  or  its  foot,  or  by 
breaking  it  at  some  intermediate  point.  The  first  piles  were 
driven  according  to  the  former  custom  of  raising  the  hammer 
to  the  top  of  the  leads  until  the  fall  reached  about  25  feet 
after  which  it  was  not  increased.  The  fall  was  gradually  di- 
minished as  successive  piles  were  driven.  Each  pile  was  pulled 
up  by  a  loo-ton  derrick  and  examined.  Nearly  every  pile 
.driven  with  a  fall  exceeding  10  feet  was  found  to  be  more  or  less 
injured,  either  by  badly  brooming  at  the  foot  or  by  breaking  at 
some  distance  higher.  A  fall  of  10  feet  could  be  depended  upon 
not  to  injure  the  pile.  To  make  sure  that  the  fall  should  not 
exceed  this  distance  the  instructions  to  the  foreman  placed 
the  limit  at  8  feet  for  a  3ooo-pound  hammer,  the  driving  to 
be  continued  until  the  penetration  should  not  exceed  i  inch 
in  the  last  three  to  five  blows  as  circumstances  might  warrant. 
Extensive  subsequent  experience  in  pile  driving  under  many 
other  conditions  confirmed  the  results  of  the  experiments  that  a 
greater  fall  than  10  feet  for  a  3ooo-pound  hammer  is  uncertain 
m  its  results  and  more  likely  than  not  to  injure  the  pile. 

The  effect  of  a  heavy  drop-hammer,  weighing  3800  pounds, 
is  seen  from  the  results  in  driving  34  piles  for  a  temporary  trestle 
at  an  under-crossing  of  a  railroad  near  Columbus,  0.,  13  piles 


ART.  1 8  OVERDRIVING  PILES  53 

or  38  percent  being  more  or  less  damaged.  Several  were  even 
telescoped,  buckled  and  bent  almost  beyond  belief,  so  as  to  be 
practically  without  value  to  sustain  loads. 

The  following  example  illustrates  conditions  which  too  fre- 
quently prevail  and  lead  to  overdriving.  No  provision  was 
made  for  an  adequate  exploration  of  sub- surf  ace  conditions.  It 
was  known,  however,  that  the  soft  mud  was  interspersed  with 
layers  of  gravel  hard-pan  of  varying  thickness.  It  was  there- 
fore decided  to  drive  the  piles  so  hard  that  it  might  be  safely 
concluded  that  they  rested  upon  a  stratum  thick  enough  to 
carry  the  required  load.  Ordinary  spruce  and  hemlock  piles 
split  and  smashed.  Finally  Nova  Scotia  spruce  piles  full  of 
solid  knots  were  obtained,  which  were  said  to  be  so  tough  as  to 
resist  splitting,  and  yet  soft  and  elastic  enough  to  absorb  the 
blows  of  the  hammer.  It  was  claimed  that  a  satisfactory 
pile  foundation  was  made  with  them.  Unfortunately  the 
opinion  prevails  too  widely  that  several  extra  blows  at  the  end 
of  the  driving  generally  secure  extra  resistance  of  the  pile  or  extra 
bearing  capacity. 

The  limit  of  safe  driving  depends  chiefly  upon  the  weight  and 
fall  of  the  hammer,  the  material  penetrated,  the  species  of  wood 
in  the  pile,  its  diameter  and  length,  and  the  protection  given 
to  the  head  of  the  pile  while  being  driven.  Whether  the  timber 
pile  is  dry  or  green  or  improperly  creosoted  will  also  need  con- 
sideration. Two  piles  have  been  driven  side  by  side  through 
the  same  ground  and  under  the  same  conditions,  so  far  as  this 
is  practically  possible;  one  pile  penetrated  to  its  full  length 
without  apparent  damage  while  the  other  "  burst  all  to  pieces," 
the  difference  in  behavior  being  due  to  the  fact  that  the  first 
pile  was  sound  while  the  second  one  had  incipient  decay  called 
'red  heart.'  The  pile  which  failed  appeared  to  penetrate  the 
ground  rapidly  and  easily,  but  the  head  showed  signs  of  dis- 
tress at  an  early  stage  of  the  driving.  The  elements  affecting 
safe  driving  are  discussed  further  in  Arts.  27,  28,  29,  33  and  35. 
Another  fruitful  reason  for  overdriving  piles  is  the  unreasonable 
specification  that  is  frequently  adopted  which  requires  driving 
to  refusal.  This  is  considered  in  Art.  38. 


54  DRIVING   TIMBER  PILES  CHAP.  II 

There  is  danger  from  overdriving  when  the  hammer  begins 
to  bounce.  Overdriving  is  also  indicated  by  the  bending,  kick- 
ing, or  staggering  of  the  pile.  When  a  pile  has  not  penetrated 
very  far  and  the  hammer  begins  to  bounce  and  the  pile  to  shiver 
and  spring  near  the  ground,  it  is  time  to  stop  driving,  unless 
the  pile  is  disproportionately  long  for  its  diameter.  In  fairly 
homogeneous  ground,  if  the  driving  becomes  hard  and  the 
hammer  starts  to  bounce  it  is  usually  wise  to  stop  driving.  If 
driving  is  continued  and  the  rate  of  penetration  is  irregular, 
it  is  probably  safe  to  assume  that  the  pile  is  either  brooming 
at  the  tip  or  fracturing  at  some  intermediate  portion  of  its 
length.  If  a  pile  suddenly  changes  direction,  there  is  but  little 
doubt  that  it  has  broken.  In  general,  when  a  pile  is  sinking 
easily  and  suddenly  stops,  and  the  hammer  commences  to 
bounce,  the  driving  should  cease,  as  it  is  probable  that  the 
pile  has  struck  a  boulder  or  some  other  obstruction.  The 
quality  of  a  pile  can  usually  be  judged  by  the  behavior  of  its 
head  under  moderate  driving.  As  the  driving  progresses,  the 
condition  of  the  head  also  gives  some  indication  regarding  the 
action  of  the  pile  below  the  surface. 

The  best  measures  to  adopt  to  prevent  injury  to  piles  by  over- 
driving include  the  use  of  a  cap  to  protect  and  guide  the  pile 
head;  the  substitution  of  the  steam-hammer  for  the  drop-ham- 
mer; the  use  of  the  water-jet  whenever  practicable;  and  an  ade- 
quate exploration  of  the  ground  to  be  penetrated.  The  steam- 
hammer  is  more  effective  than  the  drop-hammer  in  securing 
the  penetration  of  a  pile  without  injury,  because  of  the  shorter 
interval  between  blows.  Some  piles  have  taken  over  1200 
blows  without  any  sign  of  the  head  being  broomed.  The  use 
of  the  water-jet  is  one  of  the  most  effective  means  to  avoid  the 
danger  of  overdriving  since  it  reduces  the  resistance  to  pene- 
tration. Preliminary  exploration  of  sub-surface  conditions  is 
necessary  to  interpret  properly  the  behavior  of  a  pile  while 
being  driven,  as  well  as  to  determine  the  proper  length  of  pile 
and  whether  it  is  to  act  as  a  column,  or  to  support  its  load  by 
skin  friction.  In  the  preceding  paragraph  a  reference  was  made 
to  the  significance  of  an  irregular  rate  of  penetration;  it  would 


ART.  19  SPACING   OF   PILES  55 

be  entirely  different  in  stratified  material  where  the  pile  con- 
tinues to  break  through  one  thin  stratum  into  another  one  of 
different  density.  If  a  hard  crust  has  to  be  penetrated  and 
the  piles  cannot  do  so  without  injury,  it  is  better  to  use  dyna- 
mite to  break  it  up,  placing  it  by  means  of  a  pipe.  Or,  a 
double-strength  wr ought-iron  pipe,  with  a  steel  point  and  cap, 
may  be  driven  until  it  penetrates  the  hard  stratum,  and  after 
withdrawing  it,  the  timber  pile  may  be  inserted  in  the  hole  and 
driven  to  the  proper  depth.  This  method  has  been  used  to 
penetrate  a  hard  embankment  under  railroad  tracks.  In 
other  cases  the  hard  overlying  stratum  may  be  removed  by 
dredging  or  otherwise,  and  replacing  the  material  if  it  is  needed 
to  provide  lateral  resistance.  Attention  is  called  to  the  ref- 
erences on  this  topic  in  Chap.  XIX,  especially  to  the  Proceedings 
of  the  American  Railway  Engineering  Association.  It  is  often 
remarked  that  judgment  based  on  experience  will  dictate  when 
to  stop  driving.  The  training  of  the  judgment  depends  not 
so  much  on  the  amount  of  experience  as  upon  the  habit  of  care- 
ful reflection  on  the  results  of  observations  in  pile  driving  and 
of  the  probable  causes  in  each  case.  It  is  most  earnestly  to 
be  hoped  that  the  time  will  come  soon  when  it  cannot  be  truth- 
fully said  that  "the  most  prevalent  bad  practice  in  pile  driving 
is  overdriving."  See  Fig.  130  facing  page  43. 

ART.  19.     SPACING  OF  PILES 

In  good  practice  timber  piles  are  never  spaced  closer  than 
i\  feet  between  centers,  and  preferably  not  closer  than  3  feet. 
When  piles  are  supported  by  frictional  resistance  they  should  be 
driven  so  far  apart,  or  to  such  a  depth,  that  the  increased  area 
of  bearing  developed  by  the  conoid  of  pressure,  which  has 
the  required  altitude  to  contain  the  frictional  resistance,  reaches 
a  level  whose  material  will  afford  the  required  support  before 
it  intersects  the  corresponding  conoid  of  an  adjacent  pile. 
This  indicates  that  the  character  of  the  ground  at  different 
depths  should  be  known  before  the  number  of  piles  is  deter- 
mined and  any  of  them  are  driven,  or  else  the  number  required 


56  DRIVING  TIMBER   PILES  CHAP.  II 

to  support  the  given  load  must  be  changed  and  hence  the 
spacing  required. 

When  an  important  function  of  the  piles  is  to  compress  the 
ground  penetrated  by  them  a  closer  spacing  may  afford  larger 
bearing  power  at  a  given  level,  while  on  the  other  hand,  in  some 
kinds  of  material  one  or  more  extra  piles  in  a  small  group  may 
reduce  the  supporting  power  at  the  same  level.  If  piles  are 
spaced  too  close  together  the  entire  mass  of  earth  enclosed  by 
the  group  tends  to  sink  as  a  unit. 

In  discussing  this  subject  GOODRICH  states  that  "the  best 
practice  is  to  assume  a  given  load  per  pile,  to  design  all  footings 
accordingly  and  to  require  the  superintendent  of  construction 
to  provide  and  drive  piles  which  will  sustain  this  assumed  load. 
In  that  case  the  designer's  care  will  be  to  provide  just  the 
proper  number  under  each  footing  and  to  space  them  so  that 
each  pile  will  develop  its  full  proportion  of  the  given  load.  To 
this  end,  groups  should  be  made  as  nearly  circular  as  possible, 
especially  when  they  consist  of  any  considerable  number  of 
piles.  The  corner  piles  of  square  groups  of  16  piles  might  just 
as  well  be  omitted.  It  is  of  the  utmost  importance  not  to  space 
piles  too  closely  together;  or  if  close  spacing  is  necessary,  to 
drive  them  all  to  such  a  depth  that  the  bearing  power  of  the 
earth  at  that  depth  is  sufficient  to  provide  the  necessary  sup- 
port. All  the  piles  under  a  building  should  be  driven  to  the 
same  depth,  if  possible,  and  the  areas  of  groups  should  be  care- 
fully proportioned  to  the  loads  to  be  carried,  unless  the  spacing 
is  large  enough  for  each  pile  to  develop  its  full  supporting  power 
independently.  Tests  made  by  the  Department  of  Docks  and 
Ferries  of  New  York  City  prove  conclusively  that  piles  driven 
in  North  River  mud,  even  to  considerable  depths,  influence 
each  other  to  some  extent  when  6  feet  apart,  and  are  practi- 
cally a  unit  in  their  action  when  only  3  feet  apart.  A  group 
of  two  piles  thus  spaced  had  a  supporting  power  only  about 
if  times  what  a  single  pile  developed  when  properly  spaced. 

"Earth  with  35  percent  of  voids,  if  compressed  so  that  all 
voids  are  filled,  will  increase  in  density  only  54  percent.  From 
quite  a  number  of  tests  of  the  compressibility  of  soils  made  by 


ART.  19  SPACING  OF  PILES  57 

the  writer,  it  is  evident  that  a  tremendous  amount  of  energy 
is  wasted  in  pile  driving  if  the  piles  are  spaced  so  closely  that 
any  great  compressing  of  the  soil  must  be  done.  This  wasted 
energy  is  not  disclosed  in  any  pile  formula,  and  serves  to  give 
exaggerated  values  when  such  formulas  are  applied.  Con- 
siderable practical  experience  also  confirms  this  and  all  the 
other  theoretical  results  given  above.  Thus,  it  is  evident  that, 
even  with  piles  spaced  2^  feet  apart,  the  amount  of  compres- 
sion suffered  by  the  earth  is  more  than  one-quarter  of  the  maxi- 
mum possible  amount  in  many  cases  and  that  considerable 
energy  must  be  wasted  in  driving  so  closely.  A  spacing  of  3 
feet  is  much  to  be  preferred,  especially  when  it  is  seen  that 
the  theoretical  depths  to  which  it  is  necessary  to  drive  the 
piles,  in  order  to  develop  a  safe  bearing  power  of  40  ooo  pounds, 
are  16  feet  for  the  3-foot  spacing  and  26  feet  for  the  2^-foot 
spacing.  The  writer  [GOODRICH]  thinks  that  a  minimum  spac- 
ing of  not  less  than  2.7  feet  should  ever  be  allowed  and  that 
3  feet  should  be  used  whenever  possible"  (see  Trans.  Am.  Soc. 
C.  E.,  vol.  54,  page  448,  June,  1905). 

In  discussions  on  pile  driving  one  may  find  such  examples 
as  that  in  which  100  timber  piles  60  feet  long  and  12  inches  in 
diameter  at  the  butt  were  driven  into  soft  material,  2  feet 
apart  each  way,  to  sustain  a  static  load  of  600  tons,  followed  by 
the  remark  that  no  settlement  was  observed.  In  this  connec- 
tion it  may  be  well  to  quote  the  following  statement  by  WELL- 
INGTON: " Bearing  piles  should  be  spaced  at  least  3  feet  center 
to  center  each  way  if  this  gives  a  sufficient  number  to  carry  the 
load,  and  they  are  worse  than  wasted  if  driven  less  than  2\  feet 
center  to  center." 

Bearing  piles  may  be  located  in  plan  either  at  the  vertices 
of  a  series  of  squares,  or  of  a  series  of  equilateral  triangles. 
When  a  considerable  area  is  covered  the  piles  are  located  thus 
in  parallel  lines  on  the  plan,  being  opposite  to  one  another 
in  one  scheme,  and  staggered  in  the  other.  Where  the  piles 
are  staggered  the  alternate  piles  in  alternate  rows  are  sometimes 
omitted  over  a  part  of  the  area  instead  of  slightly  increasing 
the  spacing  throughout  some  rows.  As  stated  in  a  preceding 


58  DRIVING   TIMBER   PILES  CHAP.  II 

paragraph,  groups  of  piles  under  column  footings  should  be 
arranged  in  plan  as  nearly  circular  as  possible  (see  Fig.  159^). 

Since  it  is  not  always  an  easy  matter  to  hold  a  pile  closely 
to  line  it  is  of  especial  importance  to  use  range  boards  and 
transits  when  necessary  to  line  up  the  leads  of  a  floating  pile- 
driver  so  that  the  pile  may  be  started  in  correct  position. 
Telescope  leads  may  be  used  to  hold  piles  against  the  action  of 
the  current  until  the  penetration  is  sufficient  to  hold  them. 
Piles  which  are  so  crooked  that  they  cannot  be  held  fairly 
to  line  should  not  be  used.  The  stresses  which  are  produced 
in  some  piles  in  trestle  bents  or  other  structures  by  forcibly 
bending  them,  before  the  cap  and  bracing  are  attached,  are 
often  so  great  that  their  supporting  power  as  columns  is  con- 
siderably less  than  that  for  which  they  were  designed. 

ART.  20.     CUTTING  OFF  AND  REMOVING  PILES 

When  the  heads  of  piles  are  to  be  imbedded  in  a  footing  of 
concrete  it  is  unnecessary  to  have  them  cut  off  at  exactly  the 
same  level;  in  fact  it  is  often  specified  that  a  certain  proportion 
of  them  shall  be  cut  off  at  a  higher  level  than  the  rest.  The 
heads  should  be  cut  off  approximately  level  in  this  case  but 
great  precision  is  not  required. 

When  timber  caps  or  timber  grillage,  however,  are  to  transfer 
the  load  from  the  substructure  to  the  piles  it  is  important  to 
cut  off  the  piles  at  the  elevations  marked  on  the  plans  and 
that  concave,  convex  or  inclined  heads  will  not  be  accepted. 
In  the  open  air  the  cut  can  be  made  by  an  ordinary  cross-cut 
saw  upon  two  straight-edge  guides  attached  to  the  piles.  The 
next  best  method  is  to  use  a  circular  saw  mounted  upon  a 
vertical  shaft  which  is  rigidly  supported  by  a  movable  frame. 

The  piles  should  be  cut  at  such  an  elevation  that  the  top  of 
the  timber  grillage  is  below  the  ground  water  at  its  lowest 
stage.  Changes  in  this  level  due  to  probable  changes  in  the 
drainage  system  should  receive  due  consideration.  Where 
tide  water  has  access  to  piles  it  is  often  customary  to  keep  the 
timber  of  the  foundation  below  half  tide  rather  than  below  low 


ART.  20  CUTTING   OFF   AND  REMOVING  PILES  59 

tide,  since  it  will  be  kept  wet  continuously  by  the  rise  and 
fall  of  the  tide.  The  same  conditions  hold  with  respect  to  the 
heads  of  piles  imbedded  in  concrete,  otherwise  they  will  suffer 
from  dry  rot. 

When  timber  piles  have  to  be  cut  off  below  the  water  surface 
to  a  given  elevation  special  care  is  necessary  as  well  as  properly 
designed  equipment.  At  Portland,  Ore.,  256  piles  for  the  pivot 
pier  of  the  Morrison  Street  bridge  were  cut  off  as  close  as  pos- 
sible to  the  bed  of  the  river.  The  rig  designed  for  this  pur- 
pose consisted  of  a  carriage  running  on  tracks  supported  by 
solid  falsework.  On  top  of  this  was  placed  a  second  carriage 
working  across  the  first  one.  Suspended  from  the  upper  car- 
riage was  a  four-post  steel  frame  built  of  angles  and  rods,  which 
extended  down  to  the  required  depth,  and  upon  one  corner 
carried  the  shaft  to  which  a  5-foot  circular  saw  was  attached. 
The  saw  was  operated  by  an  electric  motor.  By  careful  op- 
eration the  piles  were  cut  off  to  a  practically  true  level. 

At  the  Cambridge  bridge  over  the  Charles  River  the  contract- 
ors used  a  heavily  constructed  machine  to  cut  off  foundation  piles 
from  15  to  34  feet  below  the  water  surface.  The  scow  sup- 
ported regular  pile-driver  leads  60  feet  high.  The  saw  is  42 
inches  in  diameter  and  attached  to  a  4-inch  hollow  shaft,  the 
bearings  of  which  are  supported  by  a  spud  or  vertical  timber 
14  inches  square  which  can  be  easily  raised  or  lowered  between 
the  leads.  The  driving  pulley  occupies  a  fixed  position  arid 
engages  a  continuous  spline  or  key  attached  to  the  shaft.  The 
saw  is  operated  at  a  speed  of  400  to  500  revolutions  per  minute 
by  means  of  a  40-HP.  engine  and  a  boiler  of  still  larger  capacity. 
The  usual  rate  of  cutting  lo-inch  spruce  piles  is  600  to  800  per 
day  of  10  hours,  with  a  maximum  of  600  in  a  half  day.  Hori- 
zontal range  sights  were  established  and  lines  painted  on 
the  spud  to  determine  the  proper  elevation  of  the  saw  as 
the  tide  changed. 

The  Department  of  Docks  and  Ferries  of  New  York  City 
has  an  equipment  especially  designed  and  constructed  for  rapid 
and  economical  operation.  It  has  cut  115  piles  14  inches  in 
diameter  in  five  hours,  and  a  maximum  of  u  piles  in  seven 


60  DRIVING   TIMBER   PILES  CHAP.  II 

minutes.  Its  capacity  is  only  limited  by  the  ability  of  the  crew 
to  remove  the  butts.  The  special  engine  has  a  vertical  shaft, 
double-acting  cylinders,  cranks  set  180  degrees  apart,  and  a 
5-foot  fly-wheel.  The  engine  operates  at  300  and  the  saw  at 
1000  revolutions  per  minute.  The  driving  pulley  has  a  key, 
engaging  a  seat  cut  25  feet  long  in  the  3! -inch  saw  shaft,  which 
is  34  feet  long  and  has  its  bearings  bolted  to  a  spud  52  feet  long 
suspended  between  the  leads.  The  saw  avoids  danger  of  bind- 
ing or  jamming  by  cutting  off  a  pile  before  it  can  be  stopped  by 
an  ordinary  obstacle. 

At  Superior  Entry,  Wis.,  where  foundation  piles  were  cut 
off  2  feet  above  the  bottom  of  the  lake  and  35  feet  below  low 
water,  it  was  necessary  to  secure  accurate  cutting  to  grade  to 
provide  a  uniform  bearing  for  the  timber  cribs.  The  piles 
had  been  driven  butt  down  without  extension  leads  and  a 
follower,  and  hence  their  heads  projected  above  the  water 
surface.  In  order  to  hold  the  saw  at  the  exact  elevation  a  guide 
bracket  was  attached  to  the  saw  shaft  whose  trolley  with  double- 
flanged  wheels  took  bearing  upon  an  8  by  8-inch  timber  cap  tem- 
porarily placed  on  the  adjacent  line  of  piles.  To  cut  the  last 
row  the  cap  was  placed  on  three  piles  driven  for  this  purpose. 
Errors  discovered  by  measuring  the  lengths  of  cut-off  were 
limited  to  J  inch.  With  good  weather  and  quiet  water  the 
machine  frequently  cut  45  piles  per  hour,  and  occasionally  a 
bent  of  10  piles  was  cut  in  six  minutes,  the  diameters  at  the  cut 
being  n  to  1.9  inches.  The  crew  consisted  of  seven  men  on  the 
scow  and  five  men  who  removed  the  parts  cut  off  and  placed 
the  temporary  caps  in  position.  Allowing  two  hours  to  transfer 
and  set  up  the  machine,  in  addition  to  the  actual  time  for  cutting 
230  piles,  the  work  was  done  at  an  average  cost  of  13.75  cents 
per  pile.  For  additional  details  and  illustrations  see  Engineer- 
ing News,  vol.  63,  page  696,  June  16,  1910. 

Where  only  a  small  number  of  piles  have  to  be  cut  off  or 
in  locations  where  equipment  like  that  previously  described 
cannot  be  used  on  account  of  interference  with  structures,  a 
simple  device  may  be  adopted  and  operated  by  hand.  A  rig- 
ging used  on  the  Chicago  and  Northwestern  Railway  consists 


ART.  20  CUTTING   OFF  AND  REMOVING  PILES  6 1 

of  a  triangular  frame  in  which  a  saw  4  feet  long  is  held  between 
the  ends  of  a  bent  iron  bar  2  by  J  inches  in  section  which  forms 
the  other  two  sides  of  the  triangle,  each  8  feet  long.  The 
frame  is  suspended  at  its  apex  from  a  stick  fastened  to  the 
lower  surface  of  the  stringers  of  a  pile  trestle,  and  operated 
by  hand  near  the  water  surface.  Another  device  consists  of 
a  vertical  frame  formed  by  two  timbers  crossing  each  other 
like  the  letter  X;  at  the  crossing  a  pin  is  driven  into  the  pile  to 
be  cut  off;  the  saw  is  held  between  the  lower  ends  of 
these  timbers  and  the  upper  ends  are  braced  by  a  horizontal 
timber  bolted  on  just  below  the  handles  by  means  of  which  it  is 
operated. 

At  New  Orleans  a  floating  pneumatic  caisson  has  been  em- 
ployed to  cut  off  the  piles  and  to  construct  the  timber  grillage 
upon  them  for  terminal  piers  in  the  harbor.  The  caisson  is 
surmounted  by  a  tank  for  water  ballast,  and  is  partly  supported 
by  two  barges  on  its  sides  which  are  rigidly  connected  by  a 
framework  of  Howe  trusses.  The  lower  edges  of  the  working 
chamber  were  submerged  from  15  to  18  feet.  The  construc- 
tion of  the  pneumatic  caisson  is  described  and  illustrated  in 
Engineering  Record,  vol.  54,  page  125,  Aug.  4,  1906. 

Piles  are  often  used  for  temporary  construction,  such  as  to 
support  falsework  for  the  erection  of  a  bridge,  and  have  to  be 
removed  afterward.  If  its  penetration  is  not  too  large  a  pile 
may  be  pulled  by  the  pile  line  of  a  pile-driver  or  with  the  aid 
of  block  and  tackle.  To  reduce  the  initial  resistance  the  pile 
should  be  tapped  by  the  pile-hammer  before  pulling  it;  or  if 
the  water-jet  equipment  is  available  it  may  be  used  to  loosen 
the  pile  so  that  it  can  be  easily  removed.  In  tide  water  piles 
are  sometimes  fastened  by  a  chain  to  a  scow  at  low  tide  and 
thus  pulled  by  a  rising  tide.  If  hard  ground  surrounds  a  pile 
it  may  be  started  by  securely  spiking  a  block  of  wood  on  each 
side  and  lifting  it  by  the  aid  of  two  screw  jacks. 

To  remove  the  falsework  piles  of  the  Municipal  bridge  at 
St.  Louis,  a  heavy  timber  tower  formed  of  two  bents  battered 
in  both  directions  and  thoroughly  braced  was  constructed  on 
two  barges.  "The  barges  were  placed  about  10  feet  apart  in 


62  DRIVING  TIMBER  PILES  CHAP.  II 

the  clear  so  as  to  straddle  the  double  line  of  piles  forming  a 
bent.  Two  sets  of  falls,  composed  of  four-sheave  steel  blocks, 
reeved  with  .wire  rope,  were  used  and  attached  to  the  pile  by 
means  of  chains.  After  the  pile  was  lifted  about  20  feet  by 
the  main  falls,  they  were  disconnected  and  the  pile  lifted  clear 
by  means  of  a  ranner  passing  through  a  snatch  block  attached 
to  the  lower  chord  of  the  bridge  span.  From  30  to  45  piles  per 
day  of  nine  hours  were  pulled  with  this  rig." 

In  excavating  for  a  foundation  on  reclaimed  land  in  Kansas 
City  it  was  necessary  to  pull  some  old  piles  which  averaged  18 
inches  at  the  butt  and  40  feet  in  length.  The  rig  employed 
consisted  of  four  triple  and  four  double  blocks  in  combination, 
the  if  inch  hoisting  line  being  run  to  a  25-H.P.  hoisting  en- 
gine. A  water-jet  from  a  7-5-10  duplex  pump  was  also  used. 
An  illustrated  description  of  a  sweep  pile  puller  and  of  a 
tripod  pile  puller  to  be  used  on  land  or  in  very  shallow  water 
together  with  a  statement  of  costs  may  be  found  in  Engineer- 
ing News,  vol.  49,  page  338,  April  16,  1903. 

Another  method  of  removing  piles  as  an  obstruction  in  a 
water-way  is  to  cut  them  off  with  dynamite.  A  hole  about 
i^  inches  in  diameter  is  bored  down  along  the  axis  of  the  pile 
with  a  ship  auger  and  one  or  more  sticks  of  dynamite  inserted 
and  exploded.  In  some  cases  75-percent  dynamite  has  made 
a  clean  cut.  In  one  instance  where  a  foreman  was  instructed 
to  use  70-percent  dynamite  he  used  40-percent  dynamite  as 
that  was  more  easily  obtainable.  As  a  result  the  piles  were 
merely  shattered  and  not  cut  off.  Later  on  using  two  | -pound 
sticks  of  7o-percent  and  one  of  4o-percent  dynamite  the  largest 
timber  pile  was  cut  off  and  the  top  hurled  over  50  feet  into  the 
air.  The  holes  bored  were  4!  feet  deep,  and  the  cost  was  55 
cents  per  pile  for  labor,  dynamite,  fuse  and  cap.  Dry  sand 
may  be  used  to  fill  the  hole  after  inserting  the  dynamite,  but 
does  not  need  to  be  tamped. 

In  a  report  on  the  removal  of  a  temporary  pile  bridge  to 
clear  the  river  for  floating  ice  and  logs  in  the  spring,  40-percent 
dynamite  was  stated  to  be  effective.  A  ring  was  formed  of 
telegraph  wire  which  was  large  enough  to  slip  over  a  pile,  three 


ART.  21  CHEMICAL   PRESERVATION  63 

half  sticks  of  dynamite  were  fastened  equidistant  on  the  wire 
with  a  percussion  cap  in  each.  A  fuse  was  attached  long  enoagh 
to  reach  the  bottom  of  the  river  when  the  wire  was  dropped 
over  the  pile,  and  was  connected  to  a  battery.  All  of  the  piles 
were  cut  off  clean  at  the  bottom,  making  this  method  the 
cheapest  and  quickest  way  to  remove  the  obstructing  piles. 

To  remove  a  cluster  of  13  large  pine  piles  at  Leavenworth, 
Kans.,  which  had  been  sunk  by  a  water-jet,  and  could  not  be 
palled  on  account  of  high  water  and  floating  ice,  a  3 -gallon  jug 
was  placed  in  hot  water  and  partly  filled  with  hot  sand  so  as  to 
store  as  much  heat  as  possible.  The  remaining  space  was 
filled  with  30  pounds  of  dynamite.  After  arranging  an  exploder 
and  battery,  the  jug  was  corked  and  lowered  through  a  small 
opening  in  the  center  of  the  cluster  and  on  reaching  the  sand 
bottom  at  a  depth  of  14  feet  it  was  exploded,  thus  cutting  off 
the  piles  at  the  level  of  the  jug. 

ART.  21.     CHEMICAL  PRESERVATION 

Where  the  waters  are  infested  by  marine  borers  timber  piles 
which  are  not  chemically  treated  or  mechanically  protected 
have  a  very  short  period  of  usefulness.  The  average  life  of  a 
timber  pile  on  the  Coasts  of  the  South  Atlantic,  Gulf  and  Pa- 
cific states  ranges  from  about  eight  months  to  two  years.  The 
development  and  activity  of  the  borers  is  stimulated  by  high 
temperatures,  and  hence  in  some  of  the  more  northern  coasts 
the  average  life  may  extend  to  three  or  more  years.  The  mini- 
mum life  of  service  is  considerably  shorter.  For  example,  on 
the  coast  of  California,  where  the  average  life  of  a  pile  is  esti- 
mated at  about  two  years,  a  pine  pile  15  inches  in  diameter 
has  been  eaten  off  entirely  within  eight  months;  and  on  the  Gulf 
Coast  in  Texas,  where  the  average  life  ranges  from  one  to  one 
and  one-half  years,  piles  have  had  to  be  replaced  in  within  8 
to  30  percent  of  that  time.  In  very  salty  water  and  a  hot  season 
a  pile  1 8  inches  in  diameter  may  be  entirely  honeycombed  in 
three  months.  It  is  claimed  that  in  the  vicinity  of  Puget 
Sound,  "a  stick  of  timber,  rough  sawed,  will  last  about  eight 


64  DRIVING   TIMBER   PILES  CHAP.  II 

months,  a  peeled  pile  will  last  a  year,  a  pile  with  the  bark  on  will 
last  a  year  and  a  half,  while  a  creosoted  pile  will  last  from  15 
months  to  15  years." 

The  durability  of  creosoted  timber  piles  depends  upon 
several  elements.  The  timber  must  be  of  good  quality,  free 
from  decay,  and  should  have  sufficient  sap  wood  to  take  the 
requisite  amount  of  creosote  oil.  Timber  may  be  of  such 
high  grade  according  to  standard  specifications  for  structural 
timber  as  to  be  unfit  for  chemical  treatment.  The  creosote 
oil  must  be  high  grade,  with  the  proper  chemical  constituents 
and  physical  properties,  and  the  artificial  seasoning  and  chem- 
ical treatment  have  to  be  conducted  so  as  to  secure  the  re- 
quired impregnation. 

The  artificial  seasoning  and  treatment  of  material  is  a  con- 
tinuous operation  and  occupies  from  24  to  36  hours.  After 
the  green  material  has  been  placed  in  the  cylinder,  the  doors 
are  closed  and  steam  is  admitted  into  the  cylinder  until  the 
required  steam  pressure  is  indicated  by  the  gage.  This  pressure 
is  maintained  until  the  wood  is  thoroughly  sterilized  and  the 
sap  liquefied;  the  steam  pressure  is  then  relieved  and  both  air 
and  the  remaining  steam  are  exhausted  from  the  cylinder  by 
means  of  a  powerful  vacuum  pump.  The  temperature  in  the 
cylinder  during  this  portion  of  the  treatment  is  kept  above  the 
vaporization  point  corresponding  to  the  degree  of  vacuum,  so 
that  the  liquefied  sap  is  vaporized  and  passes  off  from  the  timber 
to  the  vacuum  pump.  After  all  the  moisture  has  been  ex- 
hausted from  the  cylinder  and  the  wood  is  perfectly  dry,  the 
cylinder  is  filled  with  oil  from  an  elevated  tank.  The  oil  pres- 
sure pump  is  then  started  and  kept  in  operation  until  the  oil 
in  the  cylinder  is  under  a  specified  pressure.  This  pressure  is 
maintained  until  the  established  system  of  measurement  in- 
dicates that  the  timber  has  been  impregnated  by  the  required 
amount  of  oil.  After  relieving  the  pressure  the  cylinder  is 
opened  and  the  timber  withdrawn. 

When  the  treatment  is  carefully  done  and  the  full  amount  of 
impregnation  with  the  best  quality  of  creosote,  or  dead  oil  of 
coal  tar,  is  secured,  the  timber  will  not  be  materially  reduced 


ART.  21  CHEMICAL   PRESERVATION  65 

in  strength  and  it  will  be  protected  effectively  from  the  teredo 
navalis  and  the  limnoria  terebrans.  At  an  inspection  made 
in  1905  of  over  4000  creosoted  piles  in  the  railroad  pile  trestle 
connecting  Galveston  Island  with  the  mainland,  which  had  been 
in  service  for  10  years,  no  traces  of  decay  or  deterioration 
could  be  found  (see  Railway  Age  Gazette,  vol.  45,  page  1270, 
Oct.  30,  1908). 

In  1904  and  1905  it  became  necessary  to  replace  the  truss 
spans  of  the  bridges  over  East  and  West  Pascagoula  rivers, 
and  of  the  Rigolets  and  Chef  Menteur  crossings  on  the  New 
Orleans  and  Mobile  Division  of  the  Louisville  and  Nashville 
Railroad,  by  new  girder  bridges  and  truss  swing  spans  to  ac- 
commodate the  heavier  rolling  stock.  Examinations  by  bor- 
ing showed  so  many  of  the  creosoted  piles  which  had  been  driven 
in  1876-78  to  be  still  perfectly  sound  that  it  was  decided  to 
use  them  in  the  new  structures.  Intermediate  pile  piers  were 
driven  and  the  old  ones  reinforced  by  additional  piles,  many  of 
which  were  sunk  by  jetting.  In  the  Chef  Menteur  bridge  not 
a  single  pile  was  replaced  on  account  of  defects,  and  in  the 
other  three  bridges  the  proportion  was  less  than  10  percent. 
Of  those  rejected  and  replaced  by  new  piles  not  one  had  been 
damaged  by  the  teredo,  nor  had  the  outer  ring  penetrated  by 
the  creosote  shown  any  signs  of  deterioration,  nor  was  a  single 
pile  seriously  decayed.  The  rejected  piles  showed  an  interior 
dry  rot  which  indicated  that  they  were  not  perfectly  sound  when 
treated.  As  the  new  cut-off  level  was  several  feet  lower  than 
the  old,  and  below  the  extreme  high- tide  level,  there  was  oppor- 
tunity for  a  thorough  examination  of  each  pile's  condition 
(Engineering  News,  vol.  61,  page  277,  March  n,  1909).  These 
results  are  more  favorable  than  can  usually  be  expected.  Ex- 
tended experience  shows,  however,  that  creosoting  may  be 
depended  upon  to  protect  timber  piles  in  gulf  waters  from  10 
to  15  years,  after  which  it  is  generally  necessary  to  furnish- ad- 
ditional protection  by  enclosing  the  piles  with  terra  cotta,  con- 
crete, or  steel  pipes  as  described  in  the  next  article. 

When  this  railroad  was  built  in  1869-70,  untreated  piles 
and  timber  were  used  to  build  the  trestles  which  cross  numerous 

5 


66  DRIVING   TIMBER   PILES  CHAP.  II 

arms  of  the  Mississippi  Sound.  Before  trains  had  been  run- 
ning six  months  an  engine  was  precipitated  into  Biloxi  Bay 
where  the  green  piles  had  been  eaten  by  the  teredo.  The 
unsatisfactory  results  obtained  by  mechanical  protection  of 
piles  in  other  trestles  whose  piles  were  also  attacked  led  to  the 
decision  in  1875  to  rebuild  with  the  creosoted  piles  referred  to 
in  the  preceding  paragraph.  The  piles  were  treated  in  a  plant 
owned  and  controlled  by  the  railroad  company.  Of  5093 
piles  driven  in  1877-78  in  19  pile  trestle  bridges  617  were  still 
in  service  in  1908  as  they  were  originally  driven;  on  account  of 
settlement  868  were  either  redriven  or  were  cut  off  to  place 
framed  bents  upon  them  in  the  years  1904,  1906  or  1908;  95 
were  replaced  from  time  to  time,  including  70  in  three  trestles 
which  had  been  cut  off  by  the  teredo;  while  3513  piles  were 
protected  mechanically  in  1892-93  in  five  trestles  where  the 
action  of  the  teredo  was  especially  severe,  and  in  which  the 
95  piles  had  been  replaced. 

The  limitations  of  space  prevent  the  insertion  of  specifica- 
tions for  the  chemical  preservation  of  piles,  and  a  discussion 
of  various  methods  of  treatment,  and  of  the  tests  to  be  applied 
to  the  oil,  etc.,  and  hence  the  student  is  referred  to  the  reports 
of  the  Committee  on  Wood  Preservation  of  the  American 
Railway  Engineering  Association,  to  the  Proceedings  of  the 
American  Wood  Preservers'  Association,  and  to  some  investi- 
gations by  the  United  States  Forest  Service.  In  these  publi- 
cations the  discussions  of  the  subject  are  kept  up  to  date,  and 
the  results  of  good  practice  are  recorded. 

ART.  22.    MECHANICAL  PROTECTION 

The  marine  wood  borers  are  almost  invariably  confined  to 
salt  water.  The  portion  of  the  pile  commonly  attacked  lies 
between  mean  tide  level  and  about  4  feet  below  low  tide.  The 
extent  of  the  ravages  inside  is  not  indicated  by  the  position 
of  the  entrance  hole.  Experience  has  shown  that  any  protec- 
tion applied  to  the  surface  of  a  pile  must  extend  for  a  short  dis- 
tance above  the  high-water  line  to  an  elevation  below  the  mud 


ART.  22 


MECHANICAL  PROTECTION 


67 


line,   due  consideration  being  given   to   the  probability  of  a 
change  in  the  elevation  of  the  mud  line. 

Since   chemical   treatment  must  be  applied  to   the  entire 
length  of  the  pile,  and  is  accordingly  quite  expensive,  various 


FIG.  22,  a  to  j. 

methods  of  mechanical  protection  have  been  devised  which  are 
applied  only  to  the  vulnerable  surface  of  the  pile.  Fig.  22  is 
reproduced  from  Circular  128  of  the  United  States  Forest 
Service  entitled  Preservation  of  Piling  against  Marine  Wood 
Borers,  by  C.  STOWELL  SMITH  1908,  to  which  reference  is 


68  DRIVING   TIMBER   PILES  CHAP.  II 

made  for  further  information.  Fig.  220,  illustrates  a  pile  with 
the  bark  left  on  it,  which  affords  protection  against  marine 
borers  provided  it  remains  absolutely  intact.  Above  the  water 
line,  however,  it  offers  an  excellent  place  for  insects  and  fungi 
which  hasten  the  destruction  of  the  pile.  In  Fig.  226  an  arti- 
ficial bark  is  provided  consisting  of  thin  plank  with  close 
joints,  which  partially  eliminates  the  danger  from  insects  and 
fungi.  In  Fig.  220  the  exposed  surface  is  completely  covered 
by  nails  with  large  square  heads  as  illustrated  directly  below 
the  pile.  Fig.  22^  shows  a  coating  of  various  mixtures  of  coal 
tar,  pitch,  asphalt  and  other  ingredients,  protected  by  a  cover- 
ing of  burlap  soaked  in  the  same  mixtures.  Figs.  220  and  / 
illustrate  a  metallic  sheathing  consisting  of  riveted  thin  sheets 
of  copper,  yellow  metal,  or  zinc,  which  is  held  in  place  by 
copper  nails. 

Fig.  22g  illustrates  a  casing  of  cement  mortar  or  concrete  in 
contact  with  the  timber  pile.  The  results  obtained  and  the 
cost  depend  largely  upon  the  design  of  the  forms  and  the 
method  of  handling  the  concrete.  In  one  case  the  forms  are 
made  of  sheet  steel  in  sections  18  inches  long,  and  split  longi- 
tudinally into  halves.  Vertical  angles  are  riveted  to  these 
halves  so  that  they  may  be  clamped  together  with  rubber  gaskets 
between  them  to  make  tight  joints.  The  lower  end  of  each 
section  is  slightly  reduced  in  diameter  and  fits  tightly  into  the 
slightly  enlarged  upper  end  of  the  next  lower  section.  The 
mortar  consists  of  one  part  cement  to  two  parts  of  sand  and 
by  means  of  a  double-end  scuttle  is  placed  by  a  diver  into  each 
section  of  the  form  before  the  next  section  is  placed  in  posi- 
tion. The  lowest  section  is  placed  in  an  excavation  in -the 
bottom,  the  mortar  is  extended  up  to  mean- tide  level,  and  the 
remainder  of  the  pile  painted  with  a  wash  of  neat  cement. 
This  method  has  produced  good  results  although  it  is  more 
expensive  than  some  others. 

In  another  device  which  is  patented  the  vertical  edges  of  the 
semi-cylindrical  sections  of  galvanized  iron  are  covered  with 
compressible  material  and  are  held  together  on  each  side  by  a 
sliding  clamp  with  a  ring  at  the  top.  In  operation,  the  sec- 


ART.  22  MECHANICAL  PROTECTION  69 

tions  are  put  together  on  top  of  each  other  near  the  head  of  the 
pile  and  gradually  lowered  until  the  form  extends  to  the 
bottom  and  is  pumped  out.  After  the  form  is  rilled  and  the 
concrete  set,  the  chain  of  clamps  is  pulled  up  by  the  rings,  thus 
releasing  the  halves  of  each  section  which  are  then  hoisted  by 
the  attached  ropes.  Shells  of  concrete  without  reinforcement 
should  not  be  placed  around  the  piles  until  they  have  been 
long  enough  in  place  so  that  no  further  swelling  will  occur, 
otherwise  it  will  crack  the  concrete. 

A  different  method  which  can  only  be  used  on  new  construc- 
tion consists  in  pre-molding  a  tapering  reinforced-concrete  shell 
long  enough  to  reach  from  above  high  water  to  a  short  distance 
below  the  bottom,  and  lowering  it  over  the  pile  by  a  hoisting  line 
of  the  pile  driver.  The  weight  of  the  hammer,  or  light  taps 
with  it  on  a  suitable  cap,  serve  to  sink  the  shell  to  its  desired 
elevation.  After  wedging  the  shell  in  a  concentric  position 
about  the  pile  head  the  bottom  is  scaled  with  rich  concrete  and 
after  two  or  more  days  the  enclosed  water  is  pumped  out  and 
the  space  filled  with  lean  concrete.  This  construction  has  been 
used  where  the  wharf  superstructure  is  of  reinforced  concrete 
and  the  column  reinforcement  is  carried  down  into  the  upper 
end  of  the  annular  space  between  the  pile  and  the  shell  and  into 
which  a  richer  mixture  of  concrete  is  placed. 

In  the  harbor  at  Seattle,  Wash.,  a  lot  of  piles  were  protected 
by  a  coating  of  cement  mortar.  After  fastening  a  wrapper 
of  poultry  wire  netting  about  each  pile,  the  covering  was 
deposited  on  the  surface  to  a  thickness  of  if  to  2  inches  by 
means  of  a  cement  gun.  The  gun  was  operated  between 
tides  and  the  'gunite'  set  up  so  quickly  that  no  trouble  was 
experienced  from  the  rising  tide.  A  coating  of  gunite  rein- 
forced by  longitudinal  rods  and  wire  fabric  has  also  been  applied 
to  new  piles  over  a  part  of  their  length,  before  being  driven,  to 
serve  as  a  mechanical  protection  against  marine  borers.  In 
one  case  the  coated  lengths  were  less  than  40  percent  of  the 
lengths  of  the  piles. 

Another  type  of  protection  consists  in  slipping  sections  of 
vitrified  clay  pipe  or  of  reinforced-concrete  pipe  over  the  heads 


DRIVING   TIMBER   PILES 


CHAP.  II 


of  piles  and  filling  up  the  intervening  space  with  sand.  To 
protect  piles  in  this  manner  after  the  cap  or  superstructures 
are  in  place  requires  the  use  of  pipe  divided  longitudinally  into 
halves.  Fig.  22  k  gives  the  dimensioned  plans  of  a  patented 
concrete  pipe  of  this  kind  known  as  the  lock-joint  pipe.  The 
two  halves  are  placed  around  the  pile  and  locked  together  by 
inserting  wooden  keys,  soaked  in  hot  tar,  in  the  scarf  joints. 
The  pipes  are  molded  in  iron  forms  and  after  seasoning  are 
placed  in  position  from  a  raft  moored  alongside  of  the  piles. 
Vitrified  pipe  is  sometimes  used  in  a  similar  manner,  but  as 
these  halves  have  butt  joints  they  must  be  wired  together  and 
it  is  difficult  to  get  tight  joints  to  hold  the  sand. 


Section   C-D. 


Side  Elevation. 
FIG.   22k. 


Section  A-B. 


The  use  of  natural  bark,  nails  and  burlap  soaked  in  various 
compounds  for  protection  is  unsatisfactory  since  they  are 
easily  injured  by  floating  debris  or  by  impact  from  the  waves. 
The  artificial  bark  is  attacked  by  the  borers  and  must  be  re- 
placed before  it  becomes  so  weak  as  to  be  knocked  off  by  drift- 
wood. The  metallic  sheathing  is  more  expensive  than  chemical 
preservation  for  the  entire  length  of  piles  and  requires  costly 
repairs.  The  sheathing  of  reinforced  concrete  has  sufficient 
strength  to  resist  the  impact  of  driftwood,  and  the  mesh  rein- 
forcement usually  holds  it  in  place  even  if  it  should  become 
cracked.  Better  results  are  obtained  with  concrete  than  with 
cement  mortar.  The  mortar  or  concrete  filled  between  the 
removable  form  and  the  pile  mixes  with  the  mud  at  the  bottom 


ART.  23  COST   OF  PILE   DRIVING  71 

to  such  an  extent  that  the  lower  part  of  the  protection  frequently 
breaks  off.  It  is  impossible  to  prevent  this  entirely  without 
considerable  expense.  A  more  serious  fault  is  the  cracking 
and  breaking  off  of  the  upper  part  of  the  encasement.  Scour 
at  the  bottom  exposes  the  unprotected  wood. 

These  defects  are  avoided  by  the  use  of  pipe  with  a  sand 
filling,  as  the  pipe  slips  down  and  one  or  more  sections  can  be 
added  above  when  this  is  observed.  If  an  intermediate  section 
is  broken  attention  is  called  to  it  by  the  sand  running  out. 
Repairs  are  easily  made  by  removing  the  broken  pieces,  lower- 
ing the  upper  sections,  adding  a  new  section  on  top,  and  filling 
in  the  sand  as  before.  This  method  of  protection  has  been  suc- 
cessfully used  for  pile  trestles  on  some  railroads  since  1893. 
Reinforced-concrete  pipe  is  superior  to  vitrified  clay  pipe  on 
account  of  its  greater  resistance  to  accidental  or  other  blows. 
In  unusually  exposed  situations  cast-iron  pipes  have  been  used. 
When  creosoted  piles  have  been  standing  in  salt  water  so  long 
as  not  to  be  immune  any  more  from  marine  borers,  they  may 
be  protected  mechanically  to  prolong  their  service. 

Figs.  221  andy  illustrate  the  protection  of  piles  by  boring 
holes  into  them  and  filling  the  holes  with  a  poisonous  substance. 
This  treatment  has  been  discontinued.  For  additional  details 
the  student  is  directed  to  the  references  on  this  subject  in 
Chap.  XIX.  See  also  the  combination  piles  which  are  described 
in  Art.  47. 

ART.  23.     COST  OF  PILE  DRIVING 

So  many  elements  enter  into  the  cost  of  driving  piles  that 
it  is  difficult  to  give  costs  that  are  of  real  value  in  estimating 
unless  the  record  is  more  complete  than  is  customary  in  practice. 
Some  statements  of  the  cost  of  driving  piles  for  the  founda- 
tions of  buildings,  trestles,  docks,  bridge  piers  and  abutments, 
are  given  in  handbooks  of  cost  data  and  in  engineering  period- 
icals, but  they  can  only  be  used  with  extreme  caution  since  the 
local  conditions  and  the  methods  of  doing  the  work  are  usually 
not  given  in  sufficient  detail,  if  they  are  given  at  all. 


72  DRIVING  TIMBER   PILES  CHAP.  II 

The  time  and  cost  depend  upon  whether  a  steam-hammer 
or  a  drop-hammer  is  employed;  whether  a  suitable  cap  is  used 
to  protect  the  pile  head  and  guide  its  movement,  or  merely  a 
pile  ring;  whether  the  water-jet  is  employed  to  sink  the  piles,  or 
to  aid  the  hammer  in  driving;  whether  the  foot  must  be  pro- 
tected by  a  shoe;  whether  the  piles  are  driven  below  the  water 
surface  by  means  of  a  follower;  whether  extension  leads  are  used; 
whether  the  pile-driver  must  be  moved  over  the  timber  bracing 
of  an  excavation,  or  directly  on  the  surface  of  the  ground; 
whether  the  piles  are  creosoted  or  not,  long  or  short,  of  hard  or 
soft  timber;  driven  with  the  butt  or  tip  down,  vertically  or  on 
a  batter.  The  cost  also  depends  upon  the  type  of  pile-driver, 
the  magnitude  of  the  job,  and  the  organization  and  experience 
of  the  crew;  but  especially  upon  the  sub-surface  conditions, 
whether  the  driving  is  easy  or  hard,  and  whether  special  pre- 
cautions are  needed  to  avoid  overdriving. 

The  following  is  a  brief  summary  of  driving  piles  for  41 
trestle  bridges  averaging  101  feet  in  length  on  the  Omaha  and 
St.  Louis  Railway  in  the  late  fall  of  1889.  In  46  days  1267 
piles  were  driven  ranging  in  length  from  14  to  52  feet,  the  average 
being  24  feet.  The  penetration  varied  from  10  to  18  feet,  or 
an  average  of  14  feet.  The  working  time  each  day  with  the 
leads  of  the  track  driver  in  position  averaged  six  hours  and  32 
minutes,  and  the  time  to  raise  and  lower  the  leads,  14  minutes. 
The  average  time  required  to  drive  a  pile  was  15  minutes 
and  to  raise  or  to  lower  the  leads,  2.5  minutes.  The  average 
cost  per  linear  foot  of  the  piles  was  15  cents,  and  the  average 
cost  per  pile  in  place  was  $5.14.  The  cost  of  labor  for  the 
46  days  was  $1683.72;  and  for  fuel  and  supplies  $262.28,  or 
15.6  percent  of  that  for  the  labor  only. 

The  following  gives  an  analysis  of  the  cost  per  pile  for  the 
4383  piles  in  place  which  support  the  timber  grillage  and 
masonry  of  Fort  Montgomery  on  Lake  Champlain,  the  piles 
being  driven  in  1844-46:  Net  cost  for  machinery,  $1.22;  cost  of 
piles,  $1.40;  driving,  40  cents;  measuring,  hauling,  securing  for 
winter  and  sharpening,  18  cents;  pile  rings,  10  cents;  cutting 
off  piles  to  receive  grillage,  n  cents;  net  cost  for  other  machin- 


ART.  23  COST   OF   PILE  DRIVING  73 

ery  than  pile-drivers,  4  cents;  contingent  services  and  contin- 
gencies for  this  part  of  the  construction,  43  cents;  total,  $3.88. 
Such  an  analysis  in  still  valuable  although  prices  have  changed. 

In  the  spring  of  1902,  on  the  Chicago  and  Eastern  Indiana 
Railway,  436  piles  were  driven  varying  in  length  from  14  to 
42  feet,  aggregating  10  535  linear  feet  at  a  total  cost  for  driving 
of  $466.35  or  of  4.4  cents  per  linear  foot.  In  1906,  on  the 
Chicago,  Milwaukee,  and  St.  Paul  Railway,  the  average  cost  of 
driving  foundation  piles  on  150  jobs  was  $2.45  per  pile.  In 
different  classes  of  work  the  cost  ranged  from  $0.75  to  $7.15; 
for  piers  and  abutments,  $3.84.  This  variation  shows  the 
effect  of  differences  in  local  conditions  including  the  size  of 
the  job. 

In  building  the  railroad  trestle  to  the  Sandy  Hook  Proving 
Ground,  the  cost  of  which  was  about  $10.60  per  linear  foot  of 
track  for  a  length  of  4494  feet,  the  cost  of  driving  creosoted 
piles  was  about  15  cents  per  linear  foot.  Three  land  and  two 
water  drivers  were  employed  with  drop-hammers  weighing 
1800  to  3000  pounds.  The  averages  for  several  hundred  piles 
observed  were:  Fall,  14  feet;  number  of  blows,  175;  time,  20 
minutes;  penetration  per  blow,  i  inch.  The  minimum  total 
penetration  was  15  feet,  and  when  the  penetration  was  over 
20  feet,  the  water-jet  process  was  used.  The  piles  were  driven 
during  the  last  quarter  of  1904. 

In  the  construction  of  the  viaduct  approaches  of  the  Southern 
Railway  over  Chattahoochee  River,  completed  in  1907,  the 
cost  for  the  piles  under  the  viaduct  footings  was  found  to  be  as 
follows:  13  750  linear  feet  of  creosoted  piles,  $3812.50;  pile 
shoes,  spikes  and  rings,  $352.33;  coal,  oil,  waste,  rent  of  driver, 
etc.,  $758. 72;  labor  for  pile  driving,  $3186.31;  labor  for  sharpen- 
ing piles,  $83.70;  making  the  total  cost  per  linear  foot  59.6 
cents,  which  includes  27.7  cents  for  the  cost  of  the  creosoted 
piles.  The  cost  01  freight  and  of  train  service  is  included  in 
the  items  for  materials,  etc.  "The  high  cost  of  pile  driving 
was  due  to  the  fact  that  one  row  of  pedestals  came  beneath  the 
old  trestle  and  thus  required  considerable  manipulation  of  the 
driver  and  loss  of  time  in  working  around  the  bents.  The 


74  DRIVING   TIMBER   PILES  CHAP.  II 

actual  labor  of  driving  piles  for  the  outside  row  of  pedestals 
was  only  a  little  over  9  cents  per  linear  foot  of  piles  in  leads." 
In  some  estimates  of  cost,  the  cost  of  driving  is  taken  from  65 
to  100  percent  of  the  cost  of  untreated  piles. 


CHAPTER  III 
BEARING  POWER  OF  PILES 

ART.  24.    Pif,ES  ACTING  AS  COLUMNS 

When  piles  on  land  project  some  distance  above  the  surface 
they  are  usually  held  in  position  laterally  by  diagonal  bracing 
whenever  there  is  sufficient  room  for  it  so  that  the  pile  is  not 
subject  to  direct  bending.  An  example  of  this  construction  oc- 
curs in  pile  trestle  bents.  If  the  vertical  distance  between  points 
of  connection  for  the  bracing  is  large,  the  pile  must  be  designed 
to  provide  for  column  action. 

Piles  driven  in  water  are  frequently  not  braced  and  hence 
it  is  essential  to  design  them  with  regard  to  their  strength  as 
long  columns  since  this  may  be  the  limiting  condition,  rather 
than  the  bearing  power,  of  the  ground  penetrated.  If  the  sub- 
structure placed  upon  the  piles  is  not  held  laterally  except  by 
vertical  piles,  then  the  piles  act  like  columns  with  the  upper 
end  practically  free  and  the  lower  end  fixed  at  some  elevation 
which  depends  upon  the  material  penetrated.  To  determine 
this  elevation  is  the  principal  problem.  Usually,  it  cannot  be 
taken  at  the  bed  of  the  river  or  lake,  since  the  material  there 
is  soft  or  yielding.  Even  if  the  bottom  consists  of  firm  gravel 
and  sand  the  required  elevation  is  one  or  more  feet  below  its 
surface.  When  the  material  is  mud  or  silt  grading  slowly  into 
more  compact  material  the  upper  strata  give  relatively  little 
resistance  to  the  lateral  deflection  of  the  pile.  That  the  re- 
sistance of  such  material  is  greater  than  may  be  naturally  in- 
ferred from  its  consistency  is  proven  by  the  fact  that  at  New 
York  piles  frequently  break  off  in  case  of  trouble  at  approxi- 
mately the  mud  line  of  North  River  silt. 

It  has  been  proposed  (see  Eng.  News,  vol.  60,  page  18,  July 
2,  1908)  as  a  reasonable  assumption  to  consider  the  lower  third 
of  the  softer  strata,  which  overlie  the  hard  stratum,  to  be  effect- 

75 


76  BEARING   POWER   OF   PILES  CHAP.  Ill 

ive  in  lateral  resistance  and  to  ignore  that  of  the  upper  two- 
thirds.  This  makes  the  assumed  free  length  of  the  pile  column 
equal  to  the  distance  from  the  pile  cap  to  the  river  bottom  plus 
two-thirds  of  the  penetration  in  distinctly  soft  ground.  The 
strength  of  such  a  column  is  equivalent  to  that  of  a  column  of 
double  the  length  with  both  ends  round.  It  must  also  be  re- 
membered that  the  strength  of  a  group  of  pile  columns  has 
only  the  strength  of  one  column  multiplied  by  their  number, 
since  there  is  no  provision  made  to  resist  their  movement  longi- 
tudinally with  respect  to  one  another.  In  this  respect  they  are 
analogous  to  composite  posts.  See  JACOBY'S  Structural  De- 
tails, Arts.  49  and  50. 

It  frequently  happens  that  bearing  piles  transmit  nearly  or 
all  of  their  vertical  load  to  a  hard  substratum,  overlaid  by 
softer  material,  which  will  yield  laterally  under  pressure.  In 
all  such  cases  the  piles  should  be  designed  as  columns. 

If  the  foot  of  a  pile  bears  on  rock  and  the  overlying  material 
is  not  able  to  resist  its  lateral  displacement  it  may  be  necessary 
to  drill  shallow  holes  into  the  rock.  In  shelving  rock  this 
method  of  preventing  displacement  is  of  especial  importance. 
Sometimes  riprap  is  used  for  this  purpose,  but  its  uneven  weight 
upon  the  material  overlying  the  rock  has  been  known  to  cause 
sliding  with  disastrous  results. 

The  section  area  of  the  post  should  be  large  enough  to  pro- 
vide adequate  bearing  area  and  the  taper  of  the  timber  pile 
should  be  as  small  as  possible.  In  some  cases  it  may  be  desir- 
able to  place  the  butt  at  the  foot  of  the  pile.  The  foot  should 
not  be  pointed  unless  it  is  necessary  to  secure  penetration 
for  a  short  distance  into  material  like  hard-pan,  to  prevent  its 
lateral  displacement. 

The  greatest  care  should  be  taken  in  driving  piles  which  are 
expected  to  rest  in  bed  rock  or  penetrate  slightly  into  hard- 
pan,  in  order  to  prevent  shattering  or  crushing  the  feet  of  piles, 
otherwise  their  supporting  power  may  be  seriously  impaired. 
When  the  overlying  material  is  muck  or  silt,  or  soft,  yielding 
material  it  is  preferable  to  omit  the  resistance,  if  any,  due  to 
skin  friction  in  designing  the  pile. 


ART.  25  THE    GOODRICH   FORMULA  77 

The  conditions  described  in  the  preceding  paragraphs  often 
apply  to  falsework  piles  used  to  erect  bridges.  In  any  case 
it  is  desirable  to  brace  the  piles  effectively  by  means  of  sway 
bracing,  but  in  rivers  which  carry  a  large  amount  of  driftwood 
during  flood  seasons,  or  large  masses  of  floating  ice,  it  is  essential 
to  provide  the  piles  with  carefully  designed  sway  bracing  and 
to  add  lateral  bracing.  Experience  amply  justifies  special  cau- 
tion in  design  and  construction  for  this  purpose. 

The  unit-stress  in  the  outer  fiber  which  may  safely  be  allowed 
depends  upon  the  species  of  wood  as  for  ordinary  wooden 
columns,  but  some  reduction  is  usually  made  on  account  of  the 
piles  being  water  soaked.  Sometimes  its  value  is  reduced 
further  on  account  of  a  lower  grade  of  timber  being  employed 
having  more  knots  and  other  defects  than  are  permitted  by 
specifications  for  structural  timber.  When  no  account  is 
taken  of  the  species  of  wood,  specifications  sometimes  give  the 
working  unit-stress  in  the  outer  fiber  as  600  pounds  per  square 
inch,  reduced  for  pile  columns  to  600  (i — l/6od),  in  which  /  is 
the  unsupported  length  in  inches  and  d  the  diameter  at  the 
middle  of  the  unsupported  length  (see  Art.  38.) 

When  piles  act  as  columns  or  are  subject  to  bending  moment 
especial  care  should  be  taken  to  drive  them  accurately  in  posi- 
tion; for  if  they  have  to  be  forced  laterally  into  line  account 
must  be  taken  of  the  initial  flexural  stress  thus  produced. 

In  case  it  is  necessary  to  deposit  riprap  to  give  lateral  support 
to  piles  or  to  prevent  scour  it  is  better  practice  to  deposit  the 
riprap  first  and  drive  the  piles  through  it,  because  filling  in 
afterward  has  been  known  to  bring  such  great  lateral  pressure 
upon  piles  as  to  cause  their  failure  by  bending. 

ART.  25.     THE  GOODRICH  FORMULA 

The  most  elaborate  attempt  which  has  been  made  to  deduce 
a  general  theoretical  formula  for  the  final  resistance  of  a  timber 
pile  when  subjected  to  the  blow  of  a  drop-hammer  is  that  of 
ERNEST  P.  GOODRICH,  the  results  of  which  are  contained  in  a 
paper  entitled,  The  Supporting  Power  of  Piles,  published  in 


78  BEARING   POWER   OF   PILES  CHAP.  Ill 

Trans.  Am.  C.  E.,  vol.  48,  page  180,  Aug.,  1902.  The  phe- 
nomena of  pile  driving  which  are  taken  into  account  mathemat- 
ically in  deducing  the  formula,  in  accordance  with  the  princi- 
ples of  physics  and  mechanics,  are  those  described  in  the  fifth 
paragraph  of  Art.  5. 

It  is  then  shown  how  fourteen  other  pile-driving  formulas  may 
be  derived  from  this  general  one,  by  stating  the  various  assump- 
tions with  respect  to  its  elements  or  terms  which  are  made  in 
each  case.  That  some  of  the  assumptions  are  seriously  in  error 
is  proved  conclusively  by  the  wide  variations  in  results  obtained 
by  the  application  of  the  formulas.  The  true  values  of  some  of 
the  terms  con  be  determined  only  by  experimental  investigation. 

The  general  formula  consists  of  twenty-five  terms  besides 
several  numerical  coefficients  and  exponents,  and  is  therefore 
too  complicated  and  unwieldy  for  practical  use.  For  this  pur- 
pose, a  number  of  terms  were  evaluated  with  the  aid  of  experi- 
ments conducted  under  proper  conditions  for  pile  driving  in 
good  practice.  One  of  these  is  referred  to  in  the  sixth  para- 
graph of  Art.  5,  and  another  in  the  third  paragraph  of  Art.  28. 
By  substituting  the  values  thus  obtained,  and  inserting  suit- 
able numerical  values  for  the  dimensions  and  weights  of  the 
pile  and  hammer,  an  expression  was  derived  giving  a  direct 
relation  between  the  pressure  on  the  head  of  the  pile  when 
it  comes  to  rest,  and  the  penetration.  From  this  relation,  it 
was  found  that  for  an  allowance  of  3  percent  error  in  the 
observation  (which,  for  example,  is  a  variation  of  f  inch  for  a 
penetration  of  4  inches),  the  corresponding  error  involved  in 
the  pressure  on  the  pile  is  3.1  percent  when  the  penetration  is 
4  inches  and  23  percent  when  the  penetration  is  i  inch.  Hence 
any  terms  in  the  formula  which  involve  a  change  of  less  than 
3  percent  in  the  pressure  on  the  pile  may  be  advantageously 
omitted,  and  no  penetration  much  less  than  i  inch  can  be  trusted 
to  give  the  corresponding  pressure  within  a  reasonable  per- 
centage of  error. 

An  extreme  variation  in  the  elastic  shortening  of  the  hammer  is 
found  to  produce  a  change  of  only  0.07  percent  in  the  pressure  on 
the  pile,  and  hence  the  four  terms  relating  to  the  deformation 


ART.  25  THE  GOODRICH  FORMULA  79 

are  omitted.  The  difference  between  the  elastic  shortening 
of  a  long  soft-wood  pile  and  that  of  a  short  hard-  wood  pile 
may  cause  an  extreme  variation  in  the  pressure  on  the  head  of 
the  pile  of  about  25  percent,  and  hence  this  term  is  retained. 

After  introducing  the  experimental  values,  and  making  the 
other  changes  mentioned,  the  formula  for-  the  final  pressure 
on  the  head  of  the  pile,  as  it  comes  to  rest,  is  reduced  to 


i;'J  (i) 

in  which  p  denotes  the  penetration  of  the  pile  under  a  single 
blow,  C  the  elastic  shortening  of  the  pile  due  to  longitudinal 
compression,  Ww  the  weight  of  the  hammer,  h  the  fall  of  the 
hammer,  Rh  the  ratio  of  the  weight  of  the  hammer  to  the  com- 
bined weight  of  hammer,  pile  and  earth  moved  in  connection 
with  the  pile,  and  vr  the  ratio  of  the  work  done  in  crushing  and 
heating  the  head  of  the  pile,  to  the  total  work  done  by  the 
hammer  exclusive  of  losses  before  it  strikes  the  pile. 

The  coefficient  1.15  in  this  expression  relates  to  the  velocity 
of  the  hammer,  it  being  found  by  experiment  that  when  the 
hammer  is  operated  in  the  customary  manner  with  the  line 
from  the  engine  attached  to  it,  v2=i.i$  gh,  instead  of  v2=  igh 
for  a  free  fall  (see  Art.  28). 

This  loss  of  energy  may  be  computed  by  formula  (i)  from 
two  sets  of  observations  on  the  same  pile  for  falls  of  the  hammer 
which  do  not  differ  widely,  provided  it  be  assumed  that  both 
the  total  pressure  or  resistance  of  the  pile  and  the  loss  of  energy 
are  the  same  in  the  two  cases.  From  observations  made  on  a 
number  of  piles  GOODRICH  found  that  the  loss  of  energy  v' 
rarely  exceeded  5  percent  and  in  most  cases  was  nearly  2  per- 
cent for  piles  that  were  sound  and  well  driven.  From  a  given 
numerical  example  in  which  ^  =  3000  pounds  and  A=i8o 
inches,  the  value  of  F  is  found  by  computation  to  be  134  400 
pounds  when  z/  =  o,  and  124  800  pounds  when  z/  =  5  percent, 
or  a  reduction  of  about  7  percent.  Without  such  observation- 
and  computations,  it  is  absolutely  impossible  to  form  any  reas 
sonable  judgment  of  the  value  of  v',  or  of  its  effect. 

To  eliminate  the  value  of  C  in  formula  (i),  the  same  data 


80  BEARING  POWER   OF   PILES  CHAP.  Ill 

are  used  and  the  values  of  if  computed  from  the  formula  but 
with  C  omitted.  The  value  V  thus  obtained  for  each  pile  in- 
cludes losses  due  to  the  compression  of  the  pile,  as  well  as  to 
heating  and  crushing  its  head.  The  values  thus  found  vary 
greatly  but  average  less  than  10  percent,  even  with  some  very 
badly  broomed  piles.  By  plotting  the  percentage  of  energy 
losses  due  to  all  causes  for  the  different  falls  of  the  hammer 
used  in  the  experiments,  the  curve  shows  that  the  loss  of  energy 
increases  with  the  height  of  the  fall.  The  author  of  the  for- 
mula states,  however,  that  his  observations  tend  to  show  that 
the  terms  involving  the  compression  of  the  pile  can  be  neglected 
and  proper  compensation  be  made  by  taking  if  as  2  percent  in 
the  formula,  provided  the  piles  are  sound  and  well  driven;  but 
the  formula  is  liable  to  be  in  error  about  20  percent,  if  the  piles 
are  poorly  driven  and  the  fall  is  much  less  than  15  feet. 

By  making  these  further  substitutions,  the  formula  becomes 
F  =  o.$i$Whh(Rw—o.o2)/p.  The  term  Rw  involves  the  un- 
knowable quantity  Wg  or  the  weight  of  the  ground  moved  in 
connection  with  the  pile.  It  was  estimated  that  for  piles  700 
inches  long  and  weighing  2000  pounds,  Wg  should  not  be  taken 
less  than  1000  pounds,  this  estimate  being  based  on  observa- 
tions of  minature. piles  driven  in  a  box  of  sand  with  glass  sides, 
and  of  the  ground  found  clinging  to  actual  piles  withdrawn 
from  the  earth.  In  special  cases,  such  an  assumption  may  in- 
volve an  error  of  33  percent  and,  if  combined  with  other  cumu- 
lative errors,  the  final  value  of  F  given  by  the  formula  may  be  50 
percent  in  error.  The  opinion  was  expressed  by  its  author, 
however,  that  if  a  sound  well-driven  pile  weighing  somewhat 
less  than  the  hammer  be  tested  by  a  fall  of  about  15  feet  and 
shows  a  penetration  of  about  i  inch,  the  formula  in  its  final 
shape  will  give  the  supporting  power  of  the  pile  immediately, 
after  driving  with  a  probable  error  of  considerably  less  than 
10  percent.  Inserting  the  value  of  ^  =  0.5,  the  formula 
finally  reduces  to  the  expression/?  =  0.2  76  Whh/p,  or  by  chang- 
ing the  height  of  the  fall  from  inches  to  feet,  it  becomes 


ART.  25  THE    GOODRICH   FORMULA  8 1 

in  which  F  denotes  the  ultimate  bearing  power  in  pounds  imme- 
diately after  driving;  WH  the  weight  of  the  drop-hammer  in 
pounds;  H  the  restrained  height  of  fall  in  feet,  the  line  being 
fastened  to  the  hammer;  and  p  the  final  penetration  per  blow, 
expressed  in  inches. 

GOODRICH  recommends  "that  in  making  tests  for  the  sup- 
porting power  of  piles,  a  standard  fall  of  hammer  be  adopted 
and  specified  for  making  all  determinations,  and  that  15  feet 
be  adopted  for  the  following  reason:  (a)  This  height  of  fall 
produces  good  observable  penetration  with  any  but  very  light 
hammers,  or  for  piles  in  extremely  compact  soils;  (b)  the  pene- 
tration is  not  excessive  for  any  but  very  heavy  hammers  or  for 
piles  in  very  light  soils;  (c)  all  frames  are  large  enough  to  afford 
this  fall;  (d)  the  lost  energy  is  comparatively  small;  (e)  nearly 
all  formulas  give  nearly  the  same  values  through  this  region  of 
variation;  (f)  the  writer's  formula  is  especially  built  for  this 
fall."  After  recommending  a  specification  relating  to  the 
weight  of  hammer,  height  of  fall  and  final  penetration,  he  adds 
"that  designers  can  more  easily  determine  the  necessary  pile 
spacing  and  the  most  desirable  factor  of  safety  to  be  used  in 
individual  cases,  and  make  the  pile-drivers  follow  a  standard 
specification,  than  otherwise." 

The  description  in  this  article  is  given  at  such  length  because 
it  properly  emphasizes  certain  phenomena  of  pile  driving  which 
are  often  not  fully  appreciated,  and  in  order  that  every  one 
who  uses  the  Goodrich  formula  may  know  all  the  elements  in- 
volved in  its  deductions,  the  values  determined  by  experiment, 
the  methods  of  determining  certain  approximations,  the  practical 
basis  for  certain  assumptions,  the  relative  effect  of  different 
elements  upon  the  bearing  power,  and  the  general  limitations 
under  which  it  may  be  used  properly  as  recommended  by  its 
author.  If,  for  example,  someone  should  pay  no  heed  to  these 
limitations,  and  proceed  to  substitute  a  value  of  zero  for  the 
penetration  p,  an  infinite  value  would  be  obtained  for  the  ulti- 
mate bearing  power  F,  which  is  manifestly  absurd.  See  the 
discussion  on  the  final  penetration  per  blow  in  Art.  29. 

It  must  not  be  forgotten  in  this  connection  that  all  formulas 
6 


82  BEARING  POWER   OF   PILES  CHAP.  Ill 

for  bearing  power  are  deduced  under  the  fundamental  hypo- 
thesis that  the  material  of  which  the  pile  is  composed  can  trans- 
mit a  load  of  this  magnitude  through  its  head  and  at  least  a 
part  of  its  length.  Therefore,  the  strength  of  the  pile  under 
longitudinal  compression  invariably  limits  the  load  which  it 
can  support,  if  this  value  is  less  than  that  given  by  the  formula. 

ART.  26.     ENGINEERING  NEWS  FORMULA 

The  Engineering  News  formula  for  pile  driving  was  developed 
by  A.  M.  WELLINGTON  in  an  approximate  and  simple  manner 
as  compared  with  that  of  GOODRICH,  by  considering  the  subject 
more  from  a  purely  practical  standpoint.  The  work  done  by 
the  hammer  having  a  weight  W,  in  falling  freely  through  the 
height,  h,  is  Wh.  The  useful  work  done  upon  the  pile  is  the  prod- 
uct of  its  resistance  multiplied  by  its  penetration  under  the 
last  blow.  The  ratio  of  these  two  products  measures  the  effi- 
ciency of  the  hammer  blow,  and  depends  likewise  upon  the  pro- 
portion of  work  wasted.  The  penetration  was  called  the  'set' 
by  WELLINGTON  and  hence  designated  by  5. 

Practically,  the  energy  stored  in  the  hammer  during  its  fall 
may  be  absorbed  in  four  different  ways:  (a)  In  brooming  and 
mashing  the  pile  either  visibly  at  the  head  or  invisibly  at  the 
foot  or  at  some  other  part  of  its  length;  (b)  in  bouncing,  and  thus 
striking  two  or  more  light  blows  instead  of  one  heavy  one; 
(c)  in  compressing  elastically  the  material  of  the  pile  and  ham- 
mer; and  (d)  in  causing  the  pile  to  penetrate  against  the  resist- 
ance of  the  surrounding  earth. 

As  indicated  in  Art.  n  brooming  constitutes  a  serious  loss 
of  useful  work  whenever  it  occurs  both  directly  in  crushing  the 
fibers  of  the  wood  and  in  cushioning  the  blow.  Brooming  at 
the  foot  does  not  diminish  the  effect  of  the  blow  on  the  pile 
head  but  dissipates  it  more  or  less  without  useful  result.  It 
can  frequently  be  detected  by  a  skilled  operator  by  a  change 
in  the  behavior  of  hammer  and  pile,  but  not  always.  Bounc- 
ing of  the  hammer  invariably  means  a  waste  of  energy,  either 
because  the  pile  has  struck  a  solid  obstacle  like  a  boulder, 
which  is  soon  detected,  or  because  the  hammer  is  too  light,  or 


ART.  26  ENGINEERING   NEWS   FORMULA  83 

the  velocity  is  too  great,  or  both,  to  get  the  pile  in  motion 
before  it  reacts  elastically  with  more  force  than  the  hammer  is 
exerting  to  push  it  down.  A  very  slight  rebound  is  a  necessary 
accompaniment  of  good  pile  driving,  due  to  the  elasticity  of 
the  pile. 

Both  brooming  and  bouncing  of  the  hammer  cannot  be  pro- 
vided for  by  any  formula  to  determine  the  bearing  power  of  a 
pile.  When  the  pile  is  nearly  home  and  the  average  penetra- 
tion is  to  be  observed  for  this  purpose,  the  broomed  top  should 
be  sawed  off  to  enable  a  fresh  surface  of  unbroken  fibers  to 
receive  the  blow.  Bouncing  is  remedied  either  by  providing 
a  heavier  hammer  or  by  diminishing  the  fall.  The, elastic 
compression  of  the  pile  and  its  effect  upon  the  bearing  power 
was  fully  treated  in  the  preceding  article.  In  the  formula  now 
under  consideration  it  is  provided  for  in  the  margin  of  safety. 

At  the  instant  when  the  hammer  strikes  the  pile  the  resist- 
ance of  the  pile  and  earth  is  relatively  very  large,  but  as  the 
pile  acquires  velocity  the  resistance  rapidly  diminishes  and  then 
continues  at  some  more  or  less  uniform  value  until  the  motion 
of  the  pile  ceases.  The  reasons  for  the  high  initial  resistance 
are  the  grip  of  the  earth  upon  the  surface  of  the  pile,  due  to  its 
settling  against  it  during  the  interval  since  the  last  blow, 
and  the  excess  in  the  coefficient  of  friction  at  rest  or  at  a  very 
low  velocity  over  that  at  a  relatively  high  velocity.  The 
approximate  measure  of  the  static  bearing  power  of  the 
pile  immediately  after  driving  is  the  comparatively  uniform 
frictional  resistance  to  penetration  after  the  high  initial  resist- 
ance is  overcome.  The  initial  resistance  is  more  difficult  to 
overcome,  since  the  impact  of  the  hammer  occurs  so  suddenly 
and  it  requires  time  for  the  stress  to  be  transmitted  through 
the  fibers  of  the  pile.  These  relations  are  indicated  graphically 
in  Fig.  26  a. 

The  initial  ordinate  OY  represents  the  initial  resistance  and 
the  final  ordinate  XB  represents  the  final  resistance  as  the 
pile  comes  to  rest.  The  area  of  the  taller  rectangle  represents 
the  work  done  by  the  hammer,  and  its  altitude  is  the  mean 
resistance  Wh/s.  The  area  enclosed  by  the  full  lines  has  the 


84  BEARING   POWER   OF   PILES  CHAP.  Ill 

some  area  Wh  as  the  rectangle,  provided  no  energy  is  wasted, 
and  its  ordinate  X  B  represents  the  bearing  power  of  the  pile. 
The  probable  ultimate  bearing  power  is  accordingly  equal 
to  Wh/(s-\-c),  the  term  c  being  some  empirical  value  to  be 
added  to  the  penetration.  It  is  thus  seen  that  to  overcome 
the  large  initial  resistance  is  equivalent  to  causing  some  extra 
penetration.  The  value  of  c  is  doubtless  as  variable  as  the 
character  of  the  ground  in  which  piles  are  driven  but  it  was 
taken  by  WELLINGTON  as  i  inch,  a  value  which  he  claimed  to 

be  "based  on  extensive  obser- 
vations of  the  behavior  of  piles 
in  driving,  and  on  many  years' 
experiment  and  study  as  to  the 
general  laws  of  friction."  This 
value  means  practically  that 
the  initial  resistance  is  about 
equivalent  to  an  extra  inch  of 
penetration  after  the  pile  is  set 
in  motion.  For  convenience  of 
observation  the  fall  is  expressed 
in  feet  and  denoted  by  H,  and 
the  penetration  in  inches, 

FIG.   26a. 

whence  the  expression  becomes 

i2WH/(s-\-i}.  A  so-called  factor  of  safety  of  6  was  then  as- 
sumed since  it  was  found  to  give  loads  as  large  as  were  custo- 
mary in  practice  based  on  precedent.  The  author  made  a 
statement  four  years  afterward  that  he  had  discovered  no 
cases  where  the  factor  6  had  proved  insufficient,  either  ex- 
perimentally or  in  service;  and  that  since  it  will  in  no  case 
require  piles  to  be  driven  closer  together  than  is  customary 
and  reasonable  he  should  advise  adhering  to  it  in  all  cases 
unless  under  some  very  exceptional  circumstances,  where  the 
engineer  may  see  that  he  has  special  cause  and  justification 
for  taking  more  chances.  Accordingly,  the  Engineering  News 
formula  for  pile  driving  with  a  drop-hammer  is 

,  f   }  ^WH 

Safe  load=  — rr 

H-i 


VpL     Wh 

s+c 


ART.  27  WEIGHT   AND   FALL    OF   DROP   HAMMER  85 

in  which  W  denotes  the  weight  of  the  drop-hammer  in  pounds, 
H  the  height  of  fall  in  feet,  provided  the  hammer  falls  freely, 
and  ^  the  average  penetration  in  inches  under  the  last  few 
blows.  For  a  discussion  of  the  limitations  of  W,  H,  and  s,  see 
Arts.  27,  28  and  29. 

This  formula  was  first  published  in  Engineering  News,  vol. 
20,  page  511,  Dec.  29,  1888.  It  has  been  used  more  extensively 
in  American  practice  than  all  other  formulas  and  at  present 
(1914)  is  widely  adopted  as  standard.  The  formula  is  modified 
for  use  with  steam-hammers  by  substituting  o.i  in  place  of  the 
constant  i  in  the  denominator,  as  explained  in  Art.  30. 

ART.  27.     WEIGHT  AND  FALL  OF  DROP-HAMMER 

In  1897  a  Committee  of  the  American  Association  of  Rail- 
way Superintendents  of  Bridges  and  Buildings  recommended 
3300  pounds  as  the  best  weight  of  drop-hammer  for  general 
railroad  service.  In  hard  driving,  experience  has  frequently 
proved  that  piles  can  be  successfully  driven  with  a  4ooo-pound 
hammer  when  a  2oco-pound  hammer  fails  to  do  so. 

In  general,  the  hammer  must  be  heavy  enough  to  put  the 
pile  in  motion  after  allowing  the  pile  to  absorb  its  share  of  the 
energy  developed  in  the  fall.  The  weight  of  the  hammer  should 
never  be  less  than  the  weight  of  the  pile  and  should  preferably 
weigh  about  twice  as  much.  In  one  example  of  piles  failing 
to  sustain  without  settlement  half  the  load  they  were  designed 
to  carry,  the  hammer  used  in  driving  was  only  56  percent  of  the 
weight  of  the  pile.  In  the  best  practice  the  height  of  fall  for 
a  drop-hammer  is  limited  to  about  20  feet.  While  a  fall  of  5 
feet  or  even  less  may  be  used  in  soft  ground,  its  value  will 
most  frequently  range  between  10  and  15  feet.  If  occasionally 
a  fall  exceeding  20  feet  be  used  to  penetrate  a  hard  stratum,  it 
should  not  be  continued  long  on  the  same  pile  for  fear  of  damag- 
ing it.  A  low  fall,  or  short  drop,  has  the  additional  advantage 
of  securing  a  more  rapid  succession  of  blows,  which  in  most 
kinds  of  earth  is  advantageous  in  securing  penetration,  and  thus 
economizing  time. 

If  W  denote  the  weight  of  the  hammer  in  pounds,  and  H 


86  BEARING  POWER   OF   PILES  CHAP.  Ill 

the  height  of  its  fall  in  feet,  WE  will  represent  closely  the  work 
done  by  the  hammer  in  a  single  blow  for  free  fall.  It  is  con- 
sidered that  30000  foot-pounds  is  about  as  small  a  value  for 
WH  as  it  is  economical  to  use  in  work  of  any  magnitude  and 
that  50000  foot-pounds  should  rarely  be  exceeded  on  account 
of  the  limited  strength  of  timber. 

The  only  drawback  that  may  be  alleged  against  a  heavy 
hammer  is  the  increased  capacity  required  for  the  hoisting 
engine  and  equipment,  but  in  work  of  any  magnitude  it  is 
economical  to  provide  the  equipment  required  to  do  the  work 
expeditiously  and  well.  If  the  fall  is  too  low,  then  nearly  all 
of  the  energy  developed  is  absorbed  by  the  pile  without  produc- 
ing motion;  and  on  the  other  hand,  if  the  fall  is  too  high,  its, 
effect  is  analogous  to  that  of  a  bullet,  too  large  a  percentage  of 
the  energy  being  expended  in  crushing  the  fibers  in  the  head  of 
the  pile,  or  possibly  damaging  it  elsewhere. 

The  resistance  of  the  pile  varies  greatly  from  the  time  it  is 
struck  by  the  hammer  until  its  motion  stops.  The  mass  of 
the  pile  and  the  higher  static  friction  cause  a  high  resistance  at 
the  start,  while  afterward  the  kinetic  energy  of  the  pile  and 
the  decreased  friction  in  motion  cause  a  much  smaller  resist- 
ance. On  this  account  a  heavy  hammer  with  a  low  fall  is 
more  effective  in  securing  the  penetration  of  a  pile  than  a  light 
hammer  with  a  high  fall  and  its  accompanying  high  velocity. 
In  the  latter  case  there  is  not  sufficient  time  allowed  to  transmit 
the  stress  through  the  fibers  of  the  pile  and  hence  too  large  a 
percentage  of  the  energy  must  be  expended  at  its  head  with 
consequent  destructive  effect. 

From  another  point  of  view,  when  the  pile  is  ready  to  give 
out  the  energy  received  from  the  hammer,  to  produce  further 
penetration  at  the  foot,  it  is  necessary  to  have  a  weight  on  the 
head  to  serve  as  an  additional  reaction;  and  a  heavy  hammer 
performs  this  function  better  than  a  light  one. 

The  facts  given  above  indicate  that  the  height  of  fall  should 
be  adjusted  to  the  resilience  of  the  timber  composing  the  pile 
as  well  as  to  some  of  its  other  qualities,  including  the  strength 
in  tension  across  the  fiber,  which  measures  resistance  to  split- 


ART.  28  THE   RESTRAINED   FALL  87 

ting.  This  fact  was  recognized  practically  when  the  com- 
mittee, referred  to  at  the  beginning  of  this  article,  recommended 
that  the  fall  should  not  exceed  1 2  feet  for  cedar  piles,  and  20  feet 
for  oak  piles. 

It  materially  facilitates  the  progress  of  the  work  if  a  prelimi- 
nary test  is  made  to  discover  the  best  height  of  fall  for  the  con- 
ditions existing  at  the  given  site.  In  one  instance  where  it  was 
found  that  the  penetration  was  not  increased  by  a  higher  fall, 
the  average  for  several  hundred  piles  observed  was:  fall,  14 
feet;  number  of  blows,  175;  time,  20  minutes;  penetration  per 
blow,  i  inch. 

When  the  rope  is  fastened  to  a  drop-hammer  and  the  falling 
hammer  must  pull  the  rope  with  it  and  thereby  also  revolve 
the  drum  of  the  hoisting  engine}  a  considerable  correction  must 
be  applied  to  the  height  of  the  restrained  fall  to  reduce  it 
to  an  equivalent  free  fall.  This  subject  is  discussed  in  the  next 
article.  It  is  the  universal  practice  to  make  no  allowance  for 
the  effect  of  wind  pressure  on  the  hammer,  nor  for  the  friction 
between  hammer  and  guides  when  the  leads  are  vertical  and  in 
good  order. 

ART.  28.     THE  RESTRAINED  FALL 

In  most  of  the  formulas  for  the  bearing  power  of  piles  it  is 
assumed  that  the  drop-hammer  falls  freely.  When  the  hammer 
is  operated  by  keeping  the  line  fastened  to  it  so  that  the  hammer 
in  descending  must  overhaul  the  line  from  the  drum,  it  is  neces- 
sary to  apply  a  correction  to  the  height  of  fall  to  reduce  it  to  an 
equivalent  free  fall. 

The  following  table  gives  the  penetrations  of  three  piles, 
driven  by  different  pile-drivers  under  both  conditions  of  free 
and  restrained  fall,  as  reported  by  G.  B.  NICHOLSON.  See 
Trans.  Am.  Soc.  C.  E.,  vol.  27,  page  172,  Aug.,  1892. 

Penetration  in  feet 

Weight  of  Height  Restrained          Free 

Pile  No.  hammer  of  fall  fall  fall 

1  2470  Ibs.  40  ft.  0.5  0.7 

2  2750  Ibs.  45  ft.  0.7  0.9 

3  2500  Ibs.  46  ft.  0.32  0.4 


88  BEARING   POWER   OF   PILES  CHAP.  Ill 

On  applying  the  Engineering  News  formula  for  the  bearing 
power  of  piles  driven  with  a  drop-hammer,  it  is  found  that 
the  restrained  falls  are  equivalent  to  the  following  percentages 
of  the  corresponding  free  falls:  74.5,  79.6,  and  83.4;  the  average 
being  79.2.  If  the  Goodrich  formula  is  applied,  in  which  the 
bearing  power  is  inversely  proportional  to  the  penetration,  pro- 
vided penetrations  less  then  J  and  preferably  less  than  J  inch 
be  excluded,  the  corresponding  percentages  are  71.4,  77-8. 
and  80.0;  the  average  being  76.4. 

From  these  data  GOODRICH  computed  the  coefficients  of  the 
final  velocity  of  the  hammer  in  each  case  to  be  1.02  and  1.28, 
instead  of  2  in  the  well-known  formula  v2  =  igh.  Their  average 
is  1.15  which  agrees  with  that  obtained  by  him  in  some  exper- 
iments in  which  the  velocity  of  the  hammer  was  obtained  di- 
rectly, the  time  on  the  recording  device  being  measured  by  a 
tuning  fork  chronograph  (see  Trans.  Am.  Soc.  C.  E.,  vol.  48, 
page  202,  Aug.,  1902). 

Instances  have  been  observed  with  new  equipment,  in  which 
the  conditions  were  unfavorable,  where  the  required  correction 
required  for  restrained  fall  was  found  to  average  50  percent. 
When  it  is  known  how  readily  the  resistance  of  the  rope  and 
drum  may  be  increased  by  the  operator  of  the  hoisting  drum, 
and  which  it  is  difficult  to  guard  against  by  inspection,  it  is 
best  to  disconnect  the  rope  from  the  hammer  and  to  employ 
nippers  to  secure  a  free  fall  when  testing  the  penetration  for 
bearing  power. 

ART.  29.     FINAL  PENETRATION  PER  BLOW 

Formulas  for  the  bearing  power  of  piles  are  not  designed  for 
the  case  where  a  pile  is  driven  through  soft  yielding  material, 
like  silt  and  wet  clay,  to  a  hard  stratum  of  sand,  gravel,  hard- 
pan  or  rock,  for  then  it  acts  like  a  column  and  must  be  designed 
accordingly.  Column  action  also  exists  where  a  pile  is  driven 
through  strata  of  varying  consistency  and  the  lower  part  of 
the  pile  penetrates  a  stratum  which  is  more  compact  than  those 
which  lie  above  it.  In  this  case  the  lower  end  may  be  almost 


ART.  29  FINAL  PENETRATION   PER  BLOW  89 

completely  restrained  while  the  upper  end  may  be  restrained 
but  slightly. 

Formulas  for  bearing  power  are  intended  primarily  for  the 
general  case  in  which  the  support  of  a  pile  is  due  to  frictional 
resistance  between  the  surface  of  the  pile  and  the  surrounding 
earth.  Extended  experience  has  proved,  however,  that  their 
use  may  properly  be  extended  to  a  pile  which  receives  some 
additional  resistance  in  bearing  at  its  foot. 

The  value  of  the  penetration  to  use  in  the  formula  is  gen- 
erally taken  as  the  mean  for  the  last  five  or  ten  blows.  When 
the  drop-hammer  is  employed  no  value  less  than  J  inch  should 
be  considered  in  any  case  for  timber  piles,  and  usually  not 
less  than  J  inch  for  hard-wood  piles,  nor  less  than  i  inch  for 
soft-wood  piles.  When  the  penetration  is  smaller  than  the 
values  just  given  it  is  highly  probable  that  the  true  penetration 
of  the  foot  of  the  pile  is  not  equal  to  the  movement  of  the 
head  of  the  pile  where  the  measurement  must  necessarily 
be  made. 

Even  the  average  penetration  under  the  last  five  blows  is 
not  a  fair  measure  of  the  bearing  power  of  the  pile  at  that 
time,  unless  the  penetration  has  been  either  uniform  for  a 
number  of  blows,  or  decreasing  at  an  approximately  uniform 
rate,  and  that  it  would  continue  in  the  same  manner  for  a 
short  distance  farther.  The  last  condition  mentioned  should 
be  known  from  previous  explorations  of  the  ground.  It  is  pre- 
supposed that  the  head  of  the  pile  is  sound,  that  the  weight  of 
the  hammer  and  height  of  fall  conform  to  the  limitations 
indicated  in  Art.  27,  arid  that  the  operation  of  driving  is  not 
interrupted  materially. 

In  practice  a  penetration  of  less  than  f  inch  should  be 
regarded  with  far  more  suspicion  than  is  frequently  accorded 
to  it.  An  apparent  penetration  below  this  limit  is  more  likely 
to  be  merely  a  sinking  of  the  head  due  to  crushing  the  foot  or 
crippling  the  pile  in  some  other  part  of  its  length. 

In  hard  driving  experienced  inspectors  are  often  misled 
when  they  do  not  know  the  character  of  the  different  strata  from 
previous  explorations.  Whenever  the  observed  penetrations 


pO  BEARING  POWER   OF  PILES  CHAP.  Ill 

are  quite  irregular  caution  is  especially  necessary.  It  is  by 
no  means  difficult  to  get  an  apparent  penetration  with  the  foot 
on  solid  rock  for  a  spruce  pile  under  a  2ooo-pound  drop-ham- 
mer by  continued  driving.  Damage  due  to  overdriving  is 
discussed  at  length  in  Art.  18. 

The  value  of  the  final  penetration  per  blow  depends  upon 
the  nature  of  the  ground,  the  size  of  the  pile,  the  smoothness 
of  its  surface,  its  taper,  the  form  and  diameter  of  the  tip,  and 
the  total  penetration,  as  well  as  upon  the  weight  and  fall  of  the 
hammer  and  some  other  minor  factors,  but  extensive  tests  have 
shown  that  the  final  penetration  under  a  given  energy  of  the 
hammer  is  practically  as  good  in  determining  the  bearing 
power  of  the  pile  as  a  test  by  actual  loading. 

Whenever  a  follower  has  to  be  used  on  top  of  a  pile  as  it  is 
driven  home  and  it  is  desired  to  compute  its  bearing  power, 
it  is  necessary  to  apply  a  correction  to  the  observed  average 
penetration.  For  this  purpose  some  bests  should  be  made 
under  fairly  comparable  conditions  when  each  pile  may  be 
driven  alternately  with  and  without  the  follower. 

ART.  30.     FORMULA  FOR  STEAM-HAMMER 

It  is  observed  that  the  dynamic  effect  of  the  short  quick 
blows  of  a  steam-hammer  exceeds  that  of  the  slower  blows  and 
higher  falls  of  a  drop-hammer  more  than  a  mere  comparison  of 
the  relative  energy  developed  seems  to  warrant.  This  is  readily 
seen  if  a  3000-pound  drop-hammer  is  operated  with  a  fall  equal 
to  that  of  a  steam-hammer  having  the  same  weight  of  moving 
parts.  The  greater  efficiency  of  the  steam-hammer  is  due 
primarily  to  the  rapidity  of  its  blows,  which  does  not  permit 
the  material  penetrated  to  settle  back  against  the  pile  after 
being  shaken  up,  or  pushed  away.  As  indicated  in  Art.  32,  ex- 
perience shows  that  12  to  24  hours  rest  requires  the  number 
of  blows  per  foot  of  penetration  to  be  increased  from  6-  to  10- 
fold.  Another  effect  of  rapid  blows  is  that  before  the  pile 
comes  fully  to  rest  the  next  blow  is  delivered,  hence  the  varia- 
tion in  resistance  is  not  so  marked  as  that  illustrated  in  Fig. 


ART.  30  FORMULA  FOR  STEAM-HAMMER  91 

26  a.  Accordingly,  the  value  of  the  constant  in  the  denominator 
of  the  Engineering  News  formula  is  dependent  chiefly  upon  the 
magnitude  of  the  time  interval  between  blows.  When,  there- 
fore the  method  of  pile  driving  is  so  radically  changed  as  by 
substituting  a  steam-hammer  for  a  drop-hammer,  the  constant 
must  be  reduced  materially.  WELLINGTON  adopted  the  value 
of  o.i.  The  Engineering  News  formula  for  pile  driving  with  a 
steam-hammer  is  therefore 

2WH 

Safe  load  = 


the  significations  of  the  terms  being  the  same  as  those  given 
in  the  sixth  paragraph  of  Art.  26. 

When  its  author  published  this  formula  he  expressed  the 
opinion  that  it  was  probably  too  conservative,  but  that  the 
experimental  data  on  which  to  base  a  closer  estimate  were  not 
available.  Since  that  time  the  subject  seems  to  have  received 
but  little  experimental  study  by  engineers.  However,  as  the 
result  of  some  observations  in  pile-driving  practice  and  of  special 
tests,  the  engineering  department  of  the  Norfolk  and  Western 
Railroad  has  adopted  the  constant  of  0.3  instead  of  o.i. 

At  the  Brooklyn  Navy  Yard  two  test  piles  were  driven  under 
probably  as  nearly  equal  conditions  of  the  ground  penetrated 
as  may  be  possible  in  practice.  One  was  driven  by  a  steam- 
hammer  with  moving  parts  of  3  tons  and  a  stroke  of  3  feet, 
and  the  penetration  per  blow  decreased  steadily  from  4  inches 
to  J  inch.  The  pile  was  20  and  14  inches  in  diameter  at  the 
butt  and  tip  respectively  and  was  driven  to  a  total  penetration 
of  43  feet  in  seven  minutes  by  373  blows.  The  other  was  driven 
by  a  i-ton  drop-hammer  which  started  with  a  fall  of  ^  foot 
and  gradually  increased  to  35  feet  as  the  pile  went  down  in  the 
leads.  It  was  driven  to  a  total  penetration  of  45  feet  with 
735  blows  in  166  minutes.  The  final  penetration  was  ij  inches. 
This  pile  had  an  iron  shoe  while  the  one  driven  by  steam-ham- 
mer had  none.  According  to  the  Engineering  News  formulas  the 
corresponding  safe  loads  are  30  and  31.1  tons.  Another  pile 
with  a  penetration  of  33  feet  driven  by  the  drop-hammer  with  a 


92  BEARING  POWER   OF  PILES  CHAP.  Ill 

fall  of  30  feet  developed  an  ultimate  resistance  of  125  tons. 
Such  close  agreement  is,  however,  by  no  means  common  between 
the  results  of  driving  by  both  types  of  hammer,  since  the  effect 
of  rest  on  the  bearing  power  varies  in  different  material  and 
between  slow  and  rapid  driving.  Whether  it  is  possible  to  make 
any  close  comparison  between  the  effect  of  driving  by  steam-  and 
drop-hammers  in  all  kinds  of  earth  is  an  open  question,  since  so 
few  observations  have  been  made  with  reference  to  this  problem. 

ART.  31.     TABLES  AND  DIAGRAMS 

A  convenient  table  for  the  safe  load  on  piles,  for  a  given  weight 
of  drop-hammer,  may  be  prepared  by  placing  the  fall  in  feet  at 
the  top  of  a  column,  and  the  penetration  in  inches  at  the  left 
end  of  a  line.  The  falls  may  include  each  foot  between  suitable 
limits,  while  the  penetrations  begin  with  }  inch  and  vary  by 
quarter  inches  at  first,  and  then  by  half  inches,  to  the  desired 
limit.  The  loads  may  be  expressed  in  units  of  i  kip  =  1000 
pounds,  or  in  tons  as  preferred,  and  then  inserted  in  the  table 
within  practical  limits. 

In  practice  diagrams  have  been  found  more  convenient  than 
tables  and  a  number  of  different  forms  have  been  devised.  In 
one  diagram  the  fall  is  laid  off  as  an  abscissa,  and  the  safe  load 
as  an  ordinate,  the  value  of  each  penetration  being  marked  on  a 
line  connecting  the  proper  points  of  intersection  of  vertical  and 
horizontal  coordinates.  For  the  Engineering  News  formula,  or 
GOODRICH'S  formula,  these  lines  are  straight. 

A  very  simple  one  for  use  with  a  given  weight  of  hammer  and 
a  standard  height  of  fall  may  be  constructed  by  laying  off  the 
average  penetration  as  an  abscissa  and  the  safe  load  as  an  ordi- 
nate. A  curve  is  then  drawn  connecting  the  proper  points  of 
intersection  of  horizontal  and  vertical  coordinates.  The  dia- 
gram shows  at  a  glance  what  penetration  is  required  for  a  given 
safe  load,  or  vice  versa.  For  a  steam-hammer  the  penetration  is 
preferably  expressed  by  the  number  of  blows  per  inch.  When 
driving  test  piles  for  foundations  on  the  New  York  Barge  Canal 
rectangular  diagrams  were  used  based  on  the  Engineering  News 


ART.  31 


TABLES  AND  DIAGRAMS 


93 


formulas  for  drop-and  steam-hammers  respectively.  On  the 
first  one  the  fall  of  the  hammer  is  laid  off  along  the  bottom  from 
zero  at  the  right  end  to  50  feet  at  the  left.  The  safe  load  is  laid 
off  along  the  top  from  zero  at  the  left  end  to  100  ooo  pounds  at 
the  right.  The  values  of  2WH  are  laid  off  on  the  left  side  from 
zero  at  the  bottom  to  168  ooo  foot-pounds  at  the  top.  A  series 
of  lines  radiating  from  the  lower  right  corner  are  drawn  for 
weights  of  hammer  from  1000  to  5200  pounds.  Another  series 


hsDrop  of  Hammer, Feet. 

o      ro      4».      <r>      oo      o 


o<g 


m, 

m 


5  ~\  ///. 


7 


^r 


Weight 


^6,000 its. 

5,000 1 Ls. 


±50 


2WOIbs 


libs. 


Ifr  Wbs. 


Penetration,  Last  Blow, Inches  . 
FIG.   3ia. 


of  lines  radiating  from  the  lower  left  corner  are  drawn  for  pene- 
trations from  |  inch  to  3  inches.  The  diagram  is  used  by  fol- 
lowing the  diagonal  line  for  weight  of  hammer  to  its  intersection 
with  the  vertical  line  for  the  height  of  fall;  from  this  point  a 
horizontal  line  is  followed  to  its  intersection  with  the  diagonal 
line  for  the  penetration;  on  the  top  of  the  vertical  line  through 
this  point  the  safe  load  is  stated. 

The  second  diagram  for  use  with  steam-hammers  is  con- 
structed on  the  same  principles.  The  fall  of  the  hammer  ex- 
tends to  5  feet,  the  safe  load  to  100  ooo  pounds  and  the  values 
of  2  WE  to  45  ooo  foot-pounds.  Four  weights  of  striking  parts 


94 


BEARING   POWER   OF   PILES 


CHAP.  Ill 


are  given:  550,  1800,  3000,  and  5000  pounds,  while  the  penetra- 
tions include  |  inch  in  addition  to  those  inserted  in  the  first  dia- 
gram (see  Eng.  Record,  vol.  56,  pages  720  and  721,  Dec.  28, 
1907). 

Fig.  310  illustrates  an  ingenious  diagram,  devised  by  A.  S. 
MILINOWSKI,  which  is  based  on  the  Engineering  News  formula 
for  steam-hammers.  A  line  connecting  the  point  Q  with  the 
intersection  of  the  coordinates  h  and  P  passes  through  the  cor- 
responding penetration.  On  a  full-size  diagram,  the  diagonal 
lines  are  replaced  by  a  thread  fastened  at  the  point  Q. 


Penetration  in  Inches  for  Last  10  Blows. 
O  —  ro  oJ  -fcno>-jootoo—  f3<5?ui<p~ 

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0                         15                  20             25           30        35       40      45     5( 
Bearing  Power  irTTons. 

FIG.  316. 

A  diagram  which  contains  no  radiating  lines,  and  is  very  easy 
to  read  with  precision,  may  be  constructed  on  logarithmic 
paper,  as  shown  in  Fig.  316.  The  vertical  coordinates  give  the 
total  penetration  in  inches  for  the  last  ten  blows  of  the  steam- 
hammer,  while  the  horizontal  coordinates  give  the  safe  loads. 
A  similar  diagram  for  a  drop-hammer  with  falls  of  20  feet  and 
less  is  given  in  an  article  by  E.  F.  KRIEGSMAN  in  Eng.  Rec., 
vol.  65,  page  417,  April  13,  1912. 


ART.  32  EFFECT  OF  REST  ON  BEARING  POWER  95 

ART.  32.  EFFECT  OF  REST  ON  BEARING  POWER 
In  some  kinds  of  material  like  sand  or  gravel  if  a  pile  be 
partly  driven  one  day  and  driving  is  resumed  the  next  day,  the 
resistance  as  measured  by  the  average  penetration  per  blow  at 
the  beginning  of  the  second  day's  driving  is  generally  found  to 
be  practically  the  same  as  that  at  the  close  of  the  first  day. 
This  is  not  the  case  with  other  kinds  of  material,  for  which 
increases  in  resistance  within  24  hours  of  more  than  1000  percent 
have  been  observed  in  extreme  cases. 

An  old  contractor  reports  an  illustration  of  this  phenomenon: 
An  attempt  was  made  to  reach  hard  bottom  through  a  very 
deep  marsh.  After  driving  a  35-foot  pile  another  one  of  equal 
length  was  spliced  to  it  and  also  driven  without  finding  a  hard 
stratum,  sinking  4  or  5  inches  per  blow.  After  driving  the  next 
pile  to  a  penetration  of  25  feet  it  was  time  to  quit  work,  hence  the 
pile  was  left  in  the  leads  in  that  position.  The  next  morning 
five  or  six  blows  of  the  hammer  failed  to  produce  any  appreci- 
able movement  and  accordingly  the  engineer  concluded  to 
drive  piles  about  35  or  40  feet  long  and  depend  upon  the  friction 
in  the  soft  meadow  muck  to  support  them.  The  trestle  bridge 
thus  supported  carried  its  traffic  safely  for  years,  the  locomotives 
and  cars  becoming  much  heavier  than  it  was  originally  expected 
would  ever  be  used  upon  it. 

On  the  6-mile  pile  trestle  bridge  of  the  New  Orleans  and 
Northeastern  Railroad  crossing  Lake  Pontchartrain  the  piles 
were  from  45  to  70  feet  long.  The  longer  piles  often  penetrated 
5  feet  under  their  own  weight,  3  feet  more  when  the  hammer 
rested  on  top,  20  feet  additional  at  the  rate  of  about  2  feet  per 
blow  for  low  drops,  and  finally  from  10  to  15  feet  deeper  with  a 
penetration  of  about  one-half  to  i  foot  for  a  3Ooo-pound 
hammer  dropping  10  feet.  The  driving  was  done  rapidly  by 
means  of  a  friction  drum.  It  was  observed  that  if  a  pile  was 
allowed  to  stand  several  hours  owing  to  a  breakdown  or  some 
other  cause,  several  blows  were  required  to  start  it,  but  later 
the  penetration  resumed  the  same  rate  as  before  the  period 
of  rest.  The  engineer  in  repeating  the  facts  15  years  later 
stated  that  none  of  the  piles  had  settled  under  the  traffic. 


96  BEARING  POWER   OF   PILES  CHAP.  Ill 

At  Fort  Point  Channel,  Boston,  borings  65  feet  below  low 
water  showed  only  soft  blue  clay  changing  in  a  few  instances  to 
soft  yellow  clay.  Tests  were  made  to  determine  the  increased 
frictiona)  resistance  after  a  period  of  rest.  A  spruce  pile  35 
feet  long,  17  inches  at  the  butt  and  7  inches  at  the  tip  was  driven 
20  feet  into  the  clay  by  a  236o-pound  hammer  falling  8  feet. 
The  average  penetration  for  the  last  five  blows  was  5.5  inches. 
After  four  days  rest,  the  pile  was  struck  20  blows,  giving  an  aver- 
age penetration  of  0.9  inch  for  the  first  five  blows  and  1.5  inches 
for  the  20  blows.  With  another  pile  in  slightly  softer  material 
the  average  penetration  for  five  blows  before  and  after  four  days 
rest  decreased  from  7.6  to  1.6  inches. 

In  the  upper  San  Francisco  Bay  is  a  deposit  of  very  soft  silt 
due  to  the  finest  and  lightest  tailings  from  hydraulic  mining  in 
the  Sacramento  and  San  Joaquin  rivers.  A  pile  sinks  20  to 
27  feet  in  it  by  its  own  weight,  but  with  a  total  penetration 
of-  40  to  55  feet  will  later  support  40  ooo  pounds.  If  a  pile  is 
allowed  to  rest  only  15  minutes  a  heavy  blow  from  a  drop-hammer 
will  not  move  it  perceptibly,  but  a  few  blows  in  rapid  succession 
will  start  it  at  the  old  rate.  While  attempting  to  splice  a  pile 
on  one  occasion  the  mud  settled  against  it  so  that  it  could  not 
be  driven  further  and  a  scow  with  a  displacement  of  30  tons 
could  not  lift  it.  The  friction  developed  was  200  pounds 
per  square  foot. 

These  examples  show  why  it  is  possible  to  sink  piles  in  soft 
ground  by  a  static  load  placed  upon  them  which  afterward 
will  safely  support  a  load  several  times  as  great.  Instead  of 
superimposing  a  static  load,  the  pile  may  be  pulled  down  by 
means  of  a  block  and  tackle  operated  from  a  scow.  It  is  also 
instructive  to  reflect  upon  the  fact  that  a  pile  driven  to  a  pene- 
tration of  90  feet  in  10  minutes  with  apparently  small  resistance, 
a  few  days  later  supported  a  test  load  of  40  tons,  whereas  a  pile 
of  this  length  could  not  support  it  without  lateral  support  if 
its  foot  stood  on  solid  rock. 

A  similar  decrease  in  penetration  after  rest  over  night  has 
often  been  observed  in  ground  where  the  average  penetration 
per  blow  was  less  than  an  inch.  In  one  instance  the  penetration 


ART.  33  EFFECT  OF   SUB-SURFACE   CONDITIONS  97 

was  reduced  in  the  ratio  of  2.3  to  i  and  in  another  from  2.8  to 
i.  At  the  Brooklyn  anchorage  of  the  Manhattan  bridge  it  was 
noticed  frequently  that  after  a  number  of  days  rest  the  resist- 
ance of  piles  would  develop  to  meet  the  requirements,  although 
the  driving  was  regarded  to  be  hard. 

The  increase  in  supporting  power  of  plastic  muds  or  clays  is 
due  to  the  material  settling  back  against  the  surface  of  the  pile 
which  was  disturbed  in  driving,  the  vibration  of  the  pile  tem- 
porarily enlarging  the  hole  and  thus  releasing  part  of  the 
frictional  resistance.  This  curious  physical  property  is  analo- 
gous to  that  of  India  rubber.  If  a  pin  be  forced  into  a  solid 
India-rubber  ball,  the  same  force  which  pushed  it  in  can  pull  it 
out  again,  provided  it  be  done  immediately,  but  after  waiting 
24  hours  the  force  required  will  be  about  five  times  as  great.  A 
similar  effect  is  produced  in  sand  which  for  certain  properties 
of  moisture  will  temporarily  arch  itself  laterally  over  small 
areas  so  that  the  pile  will  not  receive  pressure  until  some  time 
after  driving. 

ART.  33.    EFFECT  OF  SUB-SURFACE  CONDITIONS 

When  a  pile  is  held  in  position  entirely  by  frictional  resistance 
the  load  is  transferred  to  the  adjacent  ground  and  transmitted 
down  to  different  levels  in  widening  areas  until  a  level  is  reached 
where  the  earth  can  readily  support  the  unit  bearing  value. 
The  mass  of  ground  thus  transmitting  the  load  may  be  said  to 
form  approximately  a  conoid  of  pressure,  the  slope  of  which 
depends  upon  the  nature  of  the  ground  with  respect  to  both  the 
kind  of  material  and  its  degree  of  compactness.  When  the 
coefficient  of  frictional  resistance  is  small  the  total  penetration 
must  be  larger  or  the  pile  will  settle  under  the  load,  sometimes 
slipping  through  the  surrounding  material  and  at  other  times 
carrying  a  mass  of  the  earth  with  it. 

When  the  bearing  power  of  the  earth  chiefly  supports  the 
pile  at  its  foot  it  should  be  designed  as  a  column  as  described  in 
Art.  24.  When  the  support  is  due  mainly  to  friction  an  impor- 
tant criterion  of  its  magnitude  is  the  final  penetration  per  blow 
7 


98  BEARING  POWER   OF   PILES  CHAP.  Ill 

of  the  hammer;  but  in  first-class  practice  this  is  supplemented 
by  a  knowledge  of  the  characteristics  of  the  ground  at  the  site. 
It  is  important  to  know,  for  instance,  whether  the  resistance 
will  increase  for  some  time  to  a  maximum,  whether  it  will  remain 
nearly  or  quite  the  same,  or  whether  there  is  any  possibility  of 
its  diminishing. 

An  instructive  example  is  that  of  six  yellow  pine  piles  driven 
into  the  wet  alluvium  of  New  Orleans  which  supported  a 
turntable.  Their  diameters  were  14  and  12  inches  at  the  butt 
and  tip  respectively,  and  the  average  length  was  31  feet  below 
the  cut-off.  When  driven  by  a  2825-pound  hammer  falling  from 
30  to  35  feet,  penetrations  9.5  to  18  inches  were  obtained  under 
the  last  blow,  or  an  average  of  12.1  inches.  The  total  number 
of  blows  for  each  pile  averaged  27,  showing  that  there  was  prac- 
tically no  appreciable  compacting  of  the  ground.  The  weight 
of  the  turntable  and  the  two  courses  of  creosoted  timber 
grillage  to  which  it  was  bolted  was  36  100  pounds,  and  the 
weight  of  engines  and  tenders  ranged  from  116000  to  156000 
pounds.  No  settlement  had  been  observed  during  the  nine 
years  of  operation  after  its  construction,  when  the  case  was 
reported. 

In  another  instance  piles  60  to  70  feet  long  were  driven  into 
mud  with  a  final  penetration  of  2  feet  or  more  per  blow,  but 
examinations  for  a  number  of  years  failed  to  give  any  evidence 
of  settlement  under  traffic.  These  piles  were  used  in  some 
bridge  foundations  on  the  Boston  and  Maine  Railroad  near 
Conway  Junction,  Mass. 

It  is  particularly  important  to  know  what  the  effect  of  time 
is  upon  the  supporting  power  of  piles  when  the  penetration  per 
blow  is  very  large.  In  Art.  32  reference  was  made  to  the  very 
fine  silt  in  upper  San  Francisco  Bay.  Even  in  that  extreme  case 
the  friction  was  found  to  be  about  200  pounds  per  square  foot. 
The  piles  supporting  the  turntable  in  New  Orleans  cited  above 
developed  a  frictional  resistance  of  about  300  pounds  per  square 
foot  under  a  load  which  was  certainly  safe.  Whenever  crusts  of 
vegetable  or  of  peat-like  deposits  cover  sections  of  swamps 
which  may  be  deep  and  strong  enough  to  support  ordinary 


ART.  33  EFFECT  OF   SUB-SURFACE  CONDITIONS  99 

highway  loads  it  is  usually  necessary  to  penetrate  them  for  pile 
foundations  and  extend  the  piles  to  the  sand  or  clay  bottom. 

Piles  have  been  driven  through  10  to  18  feet  of  soft  mud  and 
15  feet  into  soft  clay,  when  it  took  three  or  four  blows  of  a  2000- 
pound  hammer  falling  6  to  1 2  feet  to  secure  a  penetration  of  i  foot. 
Immediately  after  driving,  the  piles  might  be  swayed  as  much  as 
2  feet  at  the  head  which  was  15  to  20  feet  above  the  mud  line, 
but  at  the  end  of  a  week  it  required  considerable  force  to  move 
them.  In  attempting  to  pull  piles  which  penetrated  only  5  or 
6  feet  into  the  clay  they  frequently  broke  off. 

The  effect  of  sand  upon  the  settlement  of  piles  having 
insufficient  length,  but  for  which  the  penetration  per  blow  was 
very  small,  is  described  in  Art.  34.  By  means  of  a  steam-ham- 
mer aided  by  a  water-jet,  piles  have  been  driven  33  feet  into 
quicksand,  and  apparently  might  have  been  driven  twice  that 
depth,  which  could  not  have  been  driven  to  a  quarter  of  that 
depth  by  a  drop-hammer  alone.  In  the  upper  drainage  district 
of  New  Orleans  a  sand  stratum  underlies  the  silt  at  a  depth  of 
40  feet.  In  driving  piles  they  ' bring  up'  almost  as  suddenly  as 
if  they  struck  solid  rock.  The  difficulty  of  driving  piles  in 
gravel  increases  in  proportion  to  its  fineness,  if  the  ordinary  drop- 
hammer  method  be  employed. 

Unless  sand  or  gravel  are  mixed  with  other  material  they 
are  practically  incompressible  and  have  to  be  displaced  in 
driving  piles.  On  account  of  the  danger  of  scour  it  is  often 
necessary  to  secure  a  large  total  penetration,  and  in  such  cases 
it  is  unnecessary  to  consider  the  final  penetration  per  blow. 
The  strength  of  the  material  of  which  the  pile  is  composed  limits 
its  bearing  power. 

Engineers  who  have   closely   studied  hard-pan  and  sandy 
clays  claim  that  in  this  material  the  most  perplexing  results  I 
of  all  are  to  be  found.     No  two  hard-pans  seem  to  develop  the\ 
same  results.     The  ultimate  result  depends  not  only  upon  the,1 
percentage  of  clay  and  sand  in  the  hard-pan,  but  also  upon  the 
solubility  of  the  clay  when  brought  into  contact  with  the  local 
ground  water.     Where  piles  are  driven  through  ground  water 
overlying   hard-pan,    the  water   invariably   follows   each  pile 


100  BEARING  POWER  OF  PILES  CHAP.  Ill 

down  as  it  penetrates  the  ground,  softens  the  clay  in  contact 
with  the  surface  of  the  pile,  and  often  practically  destroys  all 
lateral  friction.  In  such  cases  the  only  point  of  support  is  at 
the  end  of  the  pile,  and  the  overhead  load  will  be  supported  by 
a  cluster  of  columns,  the  heights  of  which  are  equal  to  the 
lengths  of  the  piles. 

ART.  34.     ON  TOTAL  PENETRATION 

It  is  well  known  from  observations  in  practice  that  piles 
driven  in  sand  will  sometimes  settle  when  set  in  vibration  by 
a  live  load.  For  example,  in  a  pile  trestle  bridge,  piles  have 
settled  under  a  load  of  9  tons  each  although  they  had  been 
driven  to  an  average  penetration  of  ^  inch  with  a  i2oo-pound 
drop-hammer  falling  20  feet.  The  final  penetration  is  no  ade- 
quate index  of  the  bearing  power  of  the  pile  in  this  case,  since  the 
hammer  was  too  light  in  proportion  to  the  pile,  but  apart  from 
that,  the  primary  reason  for  its  settlement  was  its  lack  of  suf- 
ficient depth  of  total  penetration  to  prevent  the  vibration  from 
being  communicated  to  the  foot  of  the  pile.  In  another  in- 
stance piles  settled  15  inches  under  a  load  of  19  tons  each, 
which  were  supposed  to  have  been  driven  to  absolute  refusal. 

Observations  seem  to  show  that  this  tendency  for  piles  to 
settle  in  sand  is  independent  of  the  penetration  under  the  last 
blow.  Where  the  track  is  at  a  considerable  elevation  above  the 
ground  the  specified  final  penetration  per  blow  is  reached  when 
the  total  penetration  is  so  small  as  to  permit  the  pile  to  rock 
slightly  on  its  foot.  The  effective  remedy  for  such  conditions  is 
to  drive  the  piles  deeper.  This  can  readily  be  done  without 
injury  to  the  pile  since,  fortunately,  sand  is  so  well  adapted  to 
the  use  of  the  water-jet.  A  total  penetration  of  10  feet  in  sand 
may  be  sufficient  for  piles  in  a  building  foundation,  but  may  be 
insufficient  for  a  pile  trestle. 

It  is  noticed  that  if  the  longitudinal  reinforcing  bars  of  a  con- 
crete pile  are  hit  by  the  hammer  instead  of  being  protected  by 
either  plain  concrete  or  independently  reinforced  concrete  above 
it,  that  the  foot  of  the  pile  is  far  more  liable  to  be  injured  in 


ART.  35  DEGREE  OF  SECURITY  IOI 

driving.  The  steel  seems  to  transmit  vibrations  to  the  foot 
which  would  be  dissipated  otherwise  before  reaching  it.  The 
injury  to  the  foot  of  the  concrete  pile  implies  more  vibration  at 
that  point  and  therefore  makes  it  somewhat  analogous  to  the 
timber  pile  which  settles  by  the  lateral  movement  of  its  foot. 

All  the  piles  under  a  building  should  be  driven  to  the  same 
depth  if  possible  and  the  areas  of  groups  should  be  carefully 
proportioned  to  the  loads  to  be  supported  unless  the  spacing  is 
large  enough  for  each  pile  to  develop  its  full  supporting  power 
independently.  If  the  earth  is  not  uniform  in  character,  the 
piles  should  be  driven  preferably  through  the  variable  stratum 
to  one  which  is  practically  uniform. 

When  driving  piles  for  the  foundation  of  a  cylinder  pier  it 
may  not  be  possible  to  secure  the  same  depth  for  all  the  piles 
in  any  cylinder  on  account  of  the  gradually  increasing  compres- 
sion of  the  ground  unless  the  piles  first  driven  are  not  required  to 
have  as  small  a  penetration  per  blow  as  that  specified.  In  one 
example  where  the  average  penetration  of  all  the  piles  in  a 
cylinder  20  feet  in  diameter  was  3 1  feet,  the  total  penetration  for 
the  last  five  piles  driven  in  the  cylinder  averaged  24  percent  less 
than  the  penetration  for  the  first  five  piles. 

The  following  sentence  occurs  in  COOPER'S  General  Speci- 
fications for  Foundations  and  Substructures  of  [Country] 
Highway  and  Electric  Railway  Bridges  (1902):  The  minimum 
penetration  accepted  for  the  piles  should  be  about  8  to  12  feet 
in  wet  gravel,  sand,  or  stiff  clay,  and  20  to  40  feet  in  soft  clay 
or  silt.  These  values  are  apparently  intended  for  foundations 
of  substructures  supporting  light  superstructures. 

Whenever  pile  foundations  are  liable  to  scour  during  excep- 
tional floods,  provision  must  be  made  for  this  by  increasing  the 
total  penetration  beyond  the  depth  needed  to  secure  the  specified 
average  penetration  per  blow. 

ART.  35.     DEGREE  OF  SECURITY 

The  force  .F  in  equations  (i)  and  (2)  of  Art.  25  represents  the 
final  pressure  on  the  head  of  the  pile  as  it  comes  to  rest  after 


102  BEARING   POWER   OF   PILES  CHAP.  Ill 

any  blow  of  the  hammer,  but  since  an  average  value  of  the  final 
penetration  is  used  for  a  certain  number  of  blows,  it  is  assumed  to 
equal  the  ultimate  bearing  power  immediately  after  driving. 
This  bearing  power  is  liable  to  change  in  most  cases  for  earth  of 
different  kinds.  Generally  it  increases  after  driving  up  to  a 
maximum  and  this  maximum  does  not  increase  with  time.  In 
Art.' 3  2  a  number  of  examples  were  cited  to  show  how  large  an 
increase  may  occur  in  short  intervals  of  time,  but  on  the  other 
hand,  a  change  in  the  moisture  conditions  due  to  hydraulic 
constructions  may  transform  a  stratum  of  clay  into  a  slowly 
yielding  mass  which  permits  piles  to  sink  into  it  that  before 
appeared  to  have  a  solid  support,  or  deformation  in  the  ground 
of  a  contiguous  site  may  reduce  the  bearing  power  in  a  given 
site.  When  a  pile  acts  as  a  column  the  stress  in  the  outer  fiber 
due  to  its  safe  load  must  be  less  than  the  elastic  limit  of  the 
material  under  a  long  time  test  irrespective  of  the  relation 
between  the  elastic  limit  and  the  ultimate  strength  of  the  mate- 
rial for  direct  compression  in  an  ordinary  test  of  a  short  specimen. 

The  safe  load  for  a  pile  in  which  the  resistance  depends  upon 
friction  only  is  analogous  to  that  of  a  column  and  must  be  less 
than  a  load  which  will  cause  settlement  under  a  long  time  test. 
In  some  instances  it  may  be  difficult  if  not  impossible  to  deter- 
mine how  much  of  the  supporting  power  is  due  to  bearing  on  a 
solid  sub-stratum  and  how  much  to  friction  alone.  In  others 
there  is  no  guarantee  that  a  pile  will  not  steadily  sink  under  a 
heavy  quiescent  load  applied  continuously,  although  it  with- 
stands satisfactorily  the  specified  test  of  driving.  This  result 
is  especially  to  be  feared  in  clays. 

Experience  in  testing  piles  by  static  loads  placed  upon  them 
shows  that  a  load  may  cause  settlement  if  left  on  for  several 
days  or  a  week  which  produced  no  settlement  when  first  applied 
or  even  during  the  first  day,  or  a  load  may  cause  increasing 
settlement  for  a  time  but  after  a  while  no  further  settlement  will 
take  place.  What  margin  of  security  is  to  be  allowed  between 
this  load  and  the  safe  load  for  which  the  pile  is  to  be  designed 
depends  on  a  number  of  factors. 


Sometimes  the  load  to  be  supported  by  piles  is  a  dead  load 


ART.  35  DEGREE    OF   SECURITY  103 

while  in  others  it  is  a  live  load.  The  live  load  itself  may  increase 
during  the  life  of  the  foundation  as,  for  example,  that  of  loco- 
motives and  trains  passing  over  a  railroad  structure.  In  pile 
trestles  it  is  none  too  great  an  allowance  to  assume  that  the 
entire  weight  on  the  driving  wheel  base  falls  upon  each  bent  in 
succession.  In  addition  to  the  static  weight  of  the  live  load 
some  provision  must  often  be  made  for  the  dynamic  effect  due 
to  a  moving  load  or  to  the  vibration  of  machinery.  At  a  factory 
on  Fort  Point  Channel,  Boston,  the  movement  of  piles  may  be 
observed  when  the  machinery  is  in  motion.  The  allowance  thus 
made  for  foundations  is  usually  less  than  for  the  superstructures 
or  for  parts  of  the  substructure.  If  a  building  is  adjacent  to  a 
railroad  some  account  must  be  taken  of  the  fact  in  designing  its 
pile  foundation.  In  some  structures  like  that  of  a  wharf  the 
failure  of  piles  may  cause  serious  loss  of  property  or  even  loss  of 
life,  and  hence  a  larger  margin  of  security  is  needed.  In  other 
cases  it  is  difficult  to  estimate  the  probable  load.  A  higher 
load  may  often  be  used  for  piles  under  temporary  structures  than 
that  allowed  for  permanent  structures. 

A  building  may  be  subsequently  used  for  a  different  purpose 
than  that  for  which  it  was  designed.  The  building  itself  may  be 
readily  strengthened  on  this  account  but  it  may  be  impracticable 
to  increase  the  strength  of  the  foundation  without  excessive 
cost.  Such  contingencies  are  provided  for  only  in  special  cases, 
for  it  is  not  generally  economical  to  make  the  additional  invest- 
ment required.  It  makes  a  decided  difference  whether  the 
structure  to  be  supported  is  permanent  or  merely  temporary. 

The  most  important  factor  is  that  relating  to  the  nature  of 
the  ground  which  is  penetrated  by  the  piles.  The  more 
uncertainty  which  exists  in  regard  to  it,  the  larger  the  margin  of 
security  must  be.  The  character  of  the  earth  also  determines 
whether  the  bearing  power  of  all  the  piles  in  a  foundation,  or 
in  some  portion  of  it,  equals  the  bearing  power  of  one  pile  mul- 
tiplied by  the  number  of  piles.  Extra  caution  should  be  used 
when  the  penetrations  of  piles  are  quite  variable. 

Some  engineers  after  evaluating  these  several  factors  in  a 
given  case,  determine  the  safe  load  with  reference  to  the  ulti- 


104  BEARING  POWER   OF   PILES  CHAP.  Ill 

mate  strength  as  obtained  by  a  formula  for  the  bearing  power, 
while  others  fix  it  with  reference  to  the  value  obtained  from  a 
formula  that  has  been  divided  by  a  factor  to  make  it  certainly 
safe  for  the  most  unfavorable  conditions  met  in  ordinary  prac- 
tice. The  latter  hold  the  opinion  that  it  is  better  in  principle 
to  be  obliged  to  consider  carefully  whether  the  conditions  relat- 
ing to  the  foundation  have  been  so  fully  investigated  as  to 
justify  any  increase  in  the  working  load  per  pile  for  adequate 
security,  rather  than  to  start  with  a  value  which  is  certainly 
unsafe  and  reduce  that,  thus  enabling  a  man  to  deceive  himself 
with  the  notion  that  he  is  cautious,  when  he  is  really  rash. 
These  conflicting  opinions  lose  their  force  when  adequate  tests 
have  been  made  to  determine  the  character  and  the  behavior 
of  the  earth  to  be  penetrated. 

Uncertainty  with  respect  to  the  load  to  be  supported  by  the 
foundation  is  best  provided  for  by  the  addition  of  some  esti- 
mated percentage,  after  due  consideration  of  all  the  facts  and 
probabilities. 

The  statement  is  frequently  made  in  engineering  literature 
that  pile  driving  is  largely  a  matter  of  judgment  and  that  theo- 
retical considerations  have  practically  no  part  in  it.  It  should 
be  remembered,  however,  that  foundation  failures  and  lack  of 
economical  design  are  most  frequently  due  to  a  failure  to  explore 
the  sub-surface  conditions.  Under  this  condition,  the  so-called 
exercise  of  engineering  judgment  is  practically  equivalent  to 
guessing. 

It  is  interesting  to  note  the  results  of  this  method  as  indicated 
in  engineering  periodicals:  "It  is  an  established  custom  among 
engineers  to  restrict  the  loading  of  timber  piles  within  the  range 
from  6  to  1 2  tons."  "  I  note  that  there  is  a  pretty  general  work- 
ing rule  among  engineers  throughout  this  country  to  allow  a  load 
of  20  tons  each  on  all  piles  driven  to  practical  refusal." 

The  art  of  pile  driving  at  its  best  is  based  on  science.  Scien- 
tific method  consists  mainly  in  the  solution  of  a  problem  by 
analysis  into  its  component  parts  and  by  treating  each  part 
separately.  With  the  diminishing  supply  of  good  timber  piles 
and  their  increasing  cost,  the  methods  of  design  for  pile  founda- 


ART.  36  TEST  PILES  105 

tions  should  have  approximately  the  degree  of  precision  which 
is  applied  to  the  design  of  the  superstructure. 

The  margin  of  security  is  well  illustrated  in  the  following 
record  regarding  timber  piles  driven  in  1908  to  support  the  false- 
work of  Bridge  No.  5  of  the  Norfolk  and  Western  Railroad  over 
Elizabeth  River  at  Norfolk,  Va.  "The  falsework  piles  were 
driven  with  a  33<DO-pound  hammer  falling  10  feet.  They  were 
70  feet  long  and  had  a  penetration  of  about  40  feet.  The  aver- 
age penetration  at  the  last  blow  was  2  inches  and  by  the  Engi- 
neering News  formula,  the  safe  load  is  n  tons.  These  piles, 
however,  safely  carried  24  tons  per  pile  and  it  required  a  pull  of 
from  30  to  35  tons  to  pull  them  out.  The  river  bottom  is  com- 
posed of  about  10  feet  of  soft  river  silt  overlying  stiff  blue  mud 
and  sand  in  layers  of  varied  thickness";  this  formation  extend- 
ing to  a  depth  of  over  1500  feet. 

When  WELLINGTON  introduced  the  factor  of  6  in  his  formula 
to  obtain  the  safe  load,  he  practically  assumed  that  no  previous 
exploration  of  the  ground  is  ordinarily  made.  He  stated 
also  that  "the  average  factor  may  be  taken  as  somewhat  under 
four."  Some  consulting  bridge  engineers  recommend  3,  and 
others  2.5,  it  being  remembered  that  the  factor  will  probably 
be  doubled  with  the  lapse  of  time  in  many  kinds  of  earth  and 
with  a  possibility  in  some  cases  of  increasing  it  four-fold. 

It  is  interesting  in  this  connection  to  note  that  the  ultimate 
load  by  GOODRICH'S  formula  is  two  times  the  safe  load  by  the 
Engineering  News  formula  when  the  average  penetration  is 
5  inches,  2.5  times  for  a  penetration  of  2  inches,  3.3  times  for  a 
penetration  of  i  inch,  and  5  times  for  a  penetration  of  |  inch. 

ART.  36.     TEST  PILES 

The  method  of  computing  the  bearing  power  of  a  pile  by 
means  of  the  observed  final  penetration  per  blow  due  to  a 
hammer  having  a  given  weight  and  fall  is  described  in  previous 
articles  of  this  chapter.  The  practical  limitations  of  the  terms 
included  in  the  formulas  are  also  discussed  so  that  the  results 
obtained  may  conform  reasonably  to  the  practical  conditions 


106  BEARING  POWER   OF   PILES  CHAP.  Ill 

of  pile  driving.  Since  in  most  cases  the  ground  to  be  penetrated 
is  not  homogeneous  throughout  the  site,  yet  the  conditions  do 
not  differ  so  much  as  to  make  it  necessary  to  determine  the 
bearing  power  of  every  pile  nor  even  for  a  large  percentage  of 
them.  Piles  driven  to  test  the  resistance  of  the  ground,  or  to 
determine  what  length  of  pile  is  required  to  support  a  specified 
safe  load,  are  called  test  piles. 

In  order  to  secure  uniformity  in  conducting  such  tests  for  the 
foundations  of  structures  on  the  New  York  Barge  Canal, 
instructions  were  prepared  accompanied  by  suitable  diagrams 
(see  Art.  31)  to  economize  time.  The  required  loads  were  given 
on  the  plans  and  in  the  specifications.  The  instructions 
contained  the  following  items:  Test  piles  are  to  be  driven  in 
each  foundation  after  it  has  been  fully  excavated.  One  test 
pile  is  to  be  driven  for  each  500  piles,  or  less,  in  the  structure, 
but  not  less  than  three  piles  of  each  class,  for  each  structure,  and 
they  shall  be  located  so  as  to  develop  the  conditions  over  the 
entire  area.  If  the  test  is  to  be  made  with  a  steam-hammer  the 
weight  of  its  moving  parts  and  the  effective  stroke  of  the  hammer 
are  to  be  ascertained.  A  pile  is  to  be  selected  somewhat  longer 
than  that  probably  required  and  driven  in  the  proper  location. 
When  the  penetration  under  each  blow  becomes  approximately 
uniform  and  nearly  equal  to  the  value  required,  the  hammer  is 
stopped  and  its  position  marked  on  the  leads.  After  striking 
ten  blows  its  position  is  again  marked,  and  the  penetration  under 
the  last  blow  is  taken  to  be  the  average  penetration  for  the  ten 
blows.  The  safe  load  is  then  to  be  computed  by  the  Engineer- 
ing News  formula,  or  obtained  from  one  of  the  diagrams.  This 
process  is  to  be  repeated,  if  necessary,  until  the  pile  is  driven  to 
a  depth  that  gives  the  required  supporting  power.  After  meas- 
uring the  length  extending  above  the  plane  of  cut  off,  and 
deducting  this  from  the  original  length  of  the  pile,  the  required 
length  is  obtained. 

If  the  test  is  made  with  a  drop-hammer  the  elevation  of  its 
bottom  is  marked  similarly  before  and  after  the  test  blows  are 
struck.  The  engineman  is  directed  to  raise  the  hammer  to 
about  the  same  height  (15  to  20  feet)  each  time  before  letting 


ART.  36  TEST   PILES  107 

it  fall.  An  observer  standing  directly  in  front  of  the  leads  is 
to  note  the  height  reached  by  the  hammer  before  each  blow  by 
means  of  a  scale  of  feet  painted  on  the  leads.  The  average  fall 
of  the  hammer  to  be  taken  as  the  difference  between  the  mean 
of  the  elevations  of  the  two  pencil  marks  and  the  average  height 
reached  by  the  hammer.  The  penetration  for  the  ten  blows  is 
obtained  by  careful  measurement  as  before. 

Some  specifications  require  the  corresponding  average  for 
only  the  last  five  blows  to  be  taken.  Sometimes  engineers 
require  a  'trip'  to  be  used  in  driving  test  piles  with  a  drop- 
hammer,  in  order  to  insure  a  free  fall.  The  only  objection  to 
this  practice  is  that  the  driving  is  much  slower  than  that  to 
be  used  for  the  regular  piles.  In  many  cases  it  is  necessary  to 
know  the  length  of  piles  required  before  the  site  is  excavated. 
Test  pits  may  then  be  dug  to  the  elevation  of  cut-off,  and  piles 
driven  in  them  with  the  aid  of  extension  leads.  As  indicated  in 
Art.  29  penetrations  less  than  J  inch  for  a  drop-hammer  should 
be  excluded,  and  it  is  desirable  never  to  use  a  hammer  which  is 
lighter  than  the  pile.  The  head  of  the  pile  must  be  sound  and 
not  in  the  least  crushed.  The  general  observations  made  during 
the  progress  of  regular  pile  driving  later  will  indicate  whether 
an  additional  test  pile  may  be  needed  in  any  part  of  the  founda- 
tion site.  Certain  engineers  drive  test  piles  some  distance 
below  the  depth  required  to  support  the  specified  load  in  order  to 
test  the  stratum  below  the  foot  of  the  regular  piles  and  thus 
ascertain  the  conditions  more  thoroughly. 

Before  building  the  trestle  approaches  of  the  Dumbarton 
bridge  at  San  Francisco  Bay,  test  piles  were  driven  at  intervals 
of  300  feet  along  the  proposed  bridge  axis.  Under  the  mud 
from  2  to  1 8  feet  deep  was  found  a  stratum  of  fine  black  sand 
mixed  with  gravel  and  15  to  20  feet  deep,  and  which  in  turn  was 
underlaid  by  a  bed  of  hard  clay.  It  is  interesting  to  note  that 
no  trace  of  clay  was  found  by  the  Spring  Valley  Water  Company 
when  making  tests  only  about  500  feet  to  the  north  on  a  line 
parallel  to  the  Dumbarton  structure,  thus  indicating  that  it  is 
not  wise  to  fail  to  make  tests  on  a  site  because  the  results  of 
other  tests  in  the  vicinity  are  known.  When  guide  piles  are 


IO8  BEARING  POWER   OF   PILES  CHAP.  Ill 

used  in  soft  material  their  lateral  resistance  should  be  tested  to 
determine  the  length  required  on  that  account.  This  is 
unnecessary  if  the  guide  piles  are  practically  relieved  from  bend- 
ing as  cantilevers  by  horizontal  or  diagonal  bracing. 

The  final  test  of  the  bearing  power  of  a  pile  consists  in 
subjecting  it  to  a  static  load.  Two  methods  have  been  used 
in  applying  the  load,  in  one  the  load  is  balanced  on  a  single  pile 
and  in  the  other  the  load  is  placed  on  a  platform  supported  by 
three  or  four  piles.  The  latter  takes  more  time  and  involves 
greater  expense  for  hauling  and  handling  pig  iron,  brick  or  other 
loading  material.  It  requires  no  more  trouble  to  balance  the 
load  on  one  pile  than  to  guard  against  the  unequal  settlement  of 
several  piles.  Sometimes  it  may  be  more  economical  to  apply 
the  load  by  means  of  a  heavy  timber  lever,  the  short  end  of 
which  is  anchored  to  several  other  piles.  A  leverage  of  3  or  4 
to  i  may  easily  be  obtained,  and  cement  in  bags  may  be  used 
as  loading  material. 

In  case  the  piles  in  a  foundation  are  expected  to  act  as 
columns  the  results  of  loading  test  piles  should  not  be  depended 
upon  unless  they  are  sufficient  in  number  to  insure  their  action 
in  a  similar  manner,  and  they  are  stayed  against  lateral  motion. 
Since  loading  tests  in  soft  material  show  that  a  single  heavily 
loaded  pile  may  carry  down  with  it  other  unloaded  piles  driven 
at  considerable  distances  away,  it  proves  that  the  surrounding 
earth  lacks  resistance  rather  than  the  piles,  and  is  therefore 
being  tested.  Where  dependence  for  the  supporting  power  of  a 
pile  is  placed  upon  a  deep-lying  firm  stratum,  both  theory  and 
experience  have  shown  that  the  depth  of  the  stratum  below  the 
surface  has  an  appreciable  effect  on  the  actual  supporting  power 
afforded  the  bottom  of  the  pile.  In  such  a  case  E.  P.  GOODRICH 
recommends  the  sinking  of  a  large  pipe  and  after  the  soil  has 
resumed  its  natural  condition,  to  insert  through  the  pipe  a 
heavy  timber  with  a  blunt  cap  just  large  enough  to  pass  through 
to  the  earth  to  be  tested.  A  platform  on  top  of  the  timber 
can  then  be  loaded  and  accurate  observations  made  to  deter- 
mine the  compressibility  of  the  ground  in  amount  and  rate 
under  different  loads.  The  latter  should  be  alternately  increased 


ART.  36  TEST  PILES  1 09 

and  decreased  to  learn  whether  any  elasticity  exists,  and  the 
experiment  should  be  continued  over  several  days  or  weeks,  in 
order  to  ascertain  whether  the  earth  under  that  test  possesses 
any  characteristics  comparable  with  the  viscosity  of  certain 
materials.  Pipes  and  plungers  of  several  sizes  should  also  be 
employed.  The  pipe  should  be  sunk  by  dry  methods  and  accu- 
rate data  secured  of  the  weight  per  cubic  foot,  amount  of 
humidity,  and  internal  friction  coefficient  (see  Proc.  Am.  Ry. 
Eng.  Assoc.,  1910,  vol.  n,  page  217). 

In  loading  test  piles  the  weight  should  be  applied  in  incre- 
ments after  its  magnitude  is  about  two-thirds  of  the  computed 
safe  load.  An  interval  of  at  least  one  day  should  be  allowed 
between  the  application  of  the  increments  of  load  in  order  that 
the  greatest  load  may  be  known  which  just  fails  to  produce 
continued  settlement  after  the  initial  settlement  for  that  load 
has  occurred.  In  material  like  pure  sand  or  gravel  it  is 
unnecessary  to  apply  test  loads  since  its  supporting  power  is 
greater  than  that  of  the  compressive  strength  of  the  pile  itself. 

On  account  of  the  effect  of  a  period  of  rest  to  increase  the 
resistance  of  a  pile  in  soft  material  as  described  in  Art.  32,  it 
seems  reasonable  to  compare  the  bearing  power  computed  from 
the  penetration  after  rest  with  the  greatest  static  load  that  can 
be  placed  upon  the  pile  without  increase  in  settlement  for  at 
least  24  hours.  In  the  third  paragraph  of  Art.  33,  data  are 
given  relating  to  6  piles  which  carried  a  load  of  over  25000 
pounds  each  for  a  number  of  years,  but  if  the  safe  load  is  com- 
puted by  the  Engineering  News  formula  from  the  penetration 
obtained  before  a  period  of  rest,  it  is  found  to  be  only  13  ooo 
pounds.  In  another  example  a  test  pile  92  feet  long,  16  and  8 
inches  in  diameter  at  the  butt  and  tip,  was  driven  73  feet  into 
the  mud  of  San  Francisco  harbor,  the  penetration  being  3 
inches  under  the  last  blow  of  a  29oo-pound  hammer  falling  20 
feet.  The  computed  safe  load  is  29  ooo  pounds.  The  pile 
carried  90  ooo  pounds  of  pig  iron  on  a  platform  built  around  the 
pile,  and  no  further  settlement  was  perceptible  after  an  interval 
of  24  hours.  Such  a  load  may  be  properly  regarded  as  the  elas- 
tic limit  of  the  pile's  strength. 


HO  BEARING   POWER   OF   PILES  CHAP.  Ill 

In  New  York  Harbor  a  pile  with  an  average  diameter  of 
12.5  inches  and  82  feet  long  was  driven  through  30  feet  of  muck 
and  33  feet  into  loam  and  sand,  by  24  blows  of  a  38oo-pound 
drop-hammer  with  a  fall  of  10  feet,  the  penetration  under  the 
last  blow  being  9  inches.  The  computed  safe  load  is  only 
7600  pounds.  Six  days  later  a  static  load  of  20000  pounds 
(the  specified  load  to  be  carried)  was  placed  on  the  pile  and 
caused  no  settlement.  It  was  tested  again  39  days  after 
driving  by  a  5ooo-pound  drop-hammer  falling  15  feet,  and  the 
penetration  under  the  first  blow  was  found  to  be  i  inch. 

Sometimes  the  driving  of  test  piles  does  not  give  sufficient 
information  about  the  proper  location  of  the  foot  of  a  pile. 
For  example,  a  given  stratum  of  gravel  underlaid  by  soft 
material  may  be  thick  enough  to  carry  the  load  by  bearing  the 
piles  on  its  surface  but  will  not  do  so  if  the  piles  penetrate 
it  for  some  distance.  An  instructive  example  of  this  was 
quoted  by  WELLINGTON  in  Eng.  News,  vol.  22,  page  368,  Oct. 
19,  1889.  In  such  cases  and  where  test  piles  are  found  to  be  too 
expensive  on  account  of  moving  a  pile-driver  to  the  site,  a  very 
careful  investigation  should  be  made  of  the  subterranean  strata 
by  means  of  test  borings  in  several  parts  of  the  proposed  site. 
Good  wash  borings  will  generally  supply  this  information,  but 
core  borings  are  more  reliable,  as  well  as  more  expensive.  In 
certain  kinds  of  earth  borings  made  by  an  earth  auger  are 
satisfactory  and  less  expensive  (see  Art.  173).  The  borings  will 
show  the  depths  of  the  various  strata  in  different  parts  of  the 
site,  the  location  of  ground-water  level,  and  the  stratum  which 
will  afford  the  necessary  support.  In  certain  special  conditions 
of  the  ground,  however,  it  may  be  insufficient  to  have  either 
test  piles  or  borings  alone,  both  being  necessary  to  determine 
the  conditions  adequately. 

ART.  37.     PILE  RECORDS  AND  PERFORMANCE 

The  number  of  timber  piles  which  can  be  driven  by  one  pile- 
driver  gang  in  a  day  depends  upon  many  factors.  The  size  of 
the  pile;  the  depth  to  which  it  is  driven;  the  kind  of  ground 


ART.  37  PILE   RECORDS   AND  PERFORMANCE  III 

which  is  penetrated;  the  degree  of  moisture  which  it  contains; 
the  kind  of  hammer  used,  whether  a  steam-  or  drop-hammer;  the 
relation  of  the  weight  of  hammer  to  that  of  the  pile;  whether 
a  cap  or  a  ring  is  used  to  protect  the  pile;  whether  a  water- jet 
is  employed  or  not;  the  training  and  experience  of  the  crew;  as 
well  as  the  character  and  condition  of  the  pile-driver  and  its 
equipment;  all  have  their  effect  upon  the  result  obtained.  Fre- 
quently, too  much  time  is  lost  in  those  operations  which  do  not 
involve  the  action  of  the  hammer,  like  moving  the  pile-driver 
from  one  position  to  another;  getting  the  pile  to  the  driver, 
placing  it  in  the  leads,  etc. 

It  is  interesting  to  know  the  highest  record  of  performance 
attained  independent  of  conditions.  In  1901  it  was  stated  that 
the  Boston  contractors,  Holbrook,  Cabot  and  Daly,  probably 
held  the  record  for  pile  driving.  On  the  foundations  of  the  Cam- 
bridge bridge  over  the  Charles  River,  their  average  day's  work 
for  a  crew  was  considerably  over  a  hundred  piles  per  day  of  10 
hours,  while  the  highest  number  driven  in  a  single  day  of  nine 
hours  was  212.  The  piles  were  about  40  feet  long,  and  the  heads 
were  driven  with  the  aid  of  a  follower  to  an  elevation  of  18  feet 
below  low  water.  The  material  penetrated  was  a  hard  clay 
below  the  upper  stratum  of  softer  material.  The  moving  parts 
of  the  steam-hammer  employed  weighed  5000  pounds. 

As  an  example  of  the  relation  between  the  average,  the 
minimum  and  the  maximum,  the  performance  at  the  Mare 
Island  Dry  Dock  No.  2  may  be  cited.  The  average  number  of 
piles  driven  per  shift  of  eight  hours  was  35  for  a  period  of  three 
months,  74  piles  representing  the  best  day's  work.  The  timber 
piles  ranged  from  40  to  65  feet  in  length,  and  the  penetration 
varied  from  12  to  46  feet.  The  piles  were  driven  by  a  heavy 
steam-hammer  with  the  aid  of  a  4o-f oot  follower  to  such  an  eleva- 
tion that  they  could  be  cut  off  at  36  feet  below  low  water.  The 
piles  were  located  on  intersecting  lines  with  unusual  accuracy, 
the  pile-driver  being  fitted  with  sliding  extension  leads  88  feet 
long. 

Forms  of  pile  records  differ  more  or  less  according  to  the  char- 
acter of  the  structure  which  they  are  to  support.  The  American 


112  BEARING   POWER   OF   PILES  CHAP.  Ill 

Railway  Engineering  Association  adopted  a  standard  pile 
record  form  for  railroad  trestles,  after  the  examination  by  a 
committee  of  a  large  number  of  forms  used  by  different  railroads. 
It  is  published  in  the  Manual  of  the  Association.  The  four 
lines  above  the  tabular  form  are  for  the  bridge  number  or  name, 
its  location,  the  weight  and  kind  of  hammer,  the  date,  and  a 
statement  that  bents  are  numbered  from  the  north  or  east  end, 
and  that  piles  are  numbered  from  left  to  right.  The  column 
headings  are  as  follows:  Date;  bent  number;  number  of  pile; 
size  of  pile,  including  tip  end,  butt  end,  and  length;  kind  of 
wood;  length  of  cut-off;  distance  from  base  of  rail  to  the 
ground;  total  penetration;  average  for  the  last  five  blows,  of  the 
drop  of  the  hammer  and  of  the  penetration;  kind  of  soil;  and 
remarks. 

In  foundations  of  buildings,  bridge  piers,  wharves,  etc.,  the 
piles  are  usually  arranged  so  that  the  rows  in  one  direction  can 
be  lettered:  A,  B,  C,  etc.,  while  the  piles  in  each  row  are  num- 
bered. Any  pile  can  thus  be  designated  by  a  letter  combined 
with  a  number,  thus:  £19.  In  the  foundations  of  pivot  piers 
and  of  circular  buildings  the  piles  are  preferably  arranged  in 
circular  rows,  which  may  be  similarly  designated  by  letters. 

ART.  38.     SPECIFICATIONS 

When  the  extent  to  which  timber  pile  foundations  have  been 
employed  in  engineering  practice  in  America  is  taken  into 
account,  it  is  remarkable  that  the  specifications  provided  for  this 
part  of  the  construction,  with  but  few  exceptions,  have  been  so 
inadequate.  As  a  rule  they  referred  briefly  to  the  minimum 
size,  and  a  few  other  qualities  of  the  piles  that  would  be  accepted, 
and  added  a  clause  regarding  the  required  penetration  of  the 
piles,  which  in  most  cases  could  not  be  carried  out  without  dam- 
age to  the  piles,  because  the  sub-surface  conditions  had  not  been 
explored.  They  usually  omitted  any  reference  to  the  column 
action  of  the  piles,  and  gave  no  permissible  unit-stresses. 

There  is  one  expression  which  should  not  be  used  in  modern 
specifications,  and  which  has  probably  been  responsible  in  the 


ART.  38  SPECIFICATIONS  113 

past  for  more  caustic  criticisms  on  the  part  of  contractors  and 
more  unjust  flings  at  inexperienced  inspectors  than  any  other 
paragraph  in  the  whole  range  of  Engineering  specifications. 
The  expression  is  'practical  refusal'  which  was  doubtless 
expected  by  the  authors  of  specifications  to  define  the  limit  to 
which  piles  were  to  be  driven.  The  term  being  used  generally 
without  explanation,  has  been  interpreted  more  or  less  literally 
by  youthful  inspectors.  In  reality  it  is  an  ambiguous  term, 
since  one  engineer  writes  " practical  refusal  of,  say,  one  inch"; 
another,  "practical  refusal — that  is,  until  the  pile  does  not  pene- 
trate more  than  ^  inch  under  a  2ooo-pound  hammer  falling  15 
feet";  and  still  another,  "to  a  refusal  of  a  2ooo-pound  hammer 
falling  20  feet  or  its  equivalent";  while  a  fourth  modifies  it 
slightly  thus:  "  to  a  good  refusal  under  a  hammer  weighing  1500 
pounds  falling  freely  12  to  15  feet,  or  its  equivalent."  It  will 
be  noted  that  only  one  of  these  statements  is  definite.  If  an 
inexperienced  assistant  is  to  be  assigned  as  inspector  it  would 
accord  with  good  practice  in  other  departments  for  the  engineer 
in  charge  to  provide  him  with  suitable  instructions  so  that  the 
contractor  may  be  treated  with  fairness. 

The  larger  parts  of  the  specifications  for  timber  piles  adopted 
by  the  American  Railway  Engineering  Association  were 
quoted  in  Arts.  3  and  4.  The  following  specifications  on  piles 
and  pile  driving  are  reprinted,  by  permission,  as  being  one  of  the 
most  rational  and  the  most  complete  specifications  on  the  sub- 
ject. The  paragraphs  relating  to  concrete  piles  are  given  in 
Art  55. 

Extracts  from  General  Specifications  for  Bridges.  Part  III. 
Substructures  and  Concrete  Bridges.  By  J.  E.  GREINER,  1911. 

86.  Piles  shall  not  be  used  for  foundations  unless  a  penetration  of  at 
least  12  feet  in  firm  ground  or  30  feet  in  soft  ground  is  assured  by  the 
character  of  the  underlying  strata.  They  shall  generally  be  spaced  not 
closer  than  2  feet  6  inches  center  to,  center  and  their  tops  should  be  im- 
bedded at  least  6  inches  into  the  concrete  footing  course  of  the  masonry. 
When  they  pass  through  water  or  soft  ground  before  entering  firm  ground, 
their  strength  as  columns  shall  be  considered  as  well  as  their  supporting 
power  due  to  friction.  When  subjected  to  transverse  forces,  batter  piles 
shall  be  driven  in  sufficient  numbers  to  resist  the  transverse  forces  without 
8 


1 14  BEARING  POWER   OF   PILES  CHAP.  Ill 

assistance  from  the  vertical  piles.  For  foundations  of  arch  or  movable 
bridges  or  high  abutments  the  piles  shall  be  completely  embedded  in  firm 
earth,  sand  or  gravel  which  will  afford  good  lateral  support.  When  this 
is  impracticable  then  the  soft  material  shall  be  excavated  to  a  depth  of  at 
least  1 2  feet  and  heavy  stone  riprap  used  for  stiffening  and  protection. 

87.  Timber  piles,  unless  treated,  shall  not  be  used  as  an  essential  part 
of  the  foundations  above  the  ground  or  in  ground  not  permanently  wet 
or  in  water  infested  with  wood  borers.  When  of  the  quality  and  dimen- 
sions hereinafter  specified  and  when  driven  to  practical  refusal,  the  direct 
load  on  any  timber  pile  shall  not  exceed  16  tons  for  railway  bridges,  all 
movable  spans,  arches  and  high  abutments  or  20  tons  for  other  foundations. 
When  the  piles  are  in  water  and  act  as  columns,  the  maximum  stress  per 
square  inch  at  the  center  of  the  unsupported  length  shall  not  exceed  that 
permitted  by  the  following  formula: 

S  =  S'(i-l/6od) 

Where  S  =  permissible  stress  per  square  inch  at  center  of  unsupported 
length;  S'  =  600  pounds  for  longleaf  yellow  pine  or  white  oak,  and  500 
pounds  for  Douglas  fir  or  northern  pine;  /  =  unsupported  length  in  inches; 
d  =  diameter  at  center  of  the  unsupported  length  in  inches.  The  above 
is  applicable  to  lengths  between  fifteen  and  thirty  times  the  diameter 
at  center  of  unsupported  length.  When  piles  are  not  in  water  but  are 
exposed  to  view  the  above  working  stress  for  columns  may  be  increased 
50  percent. 

132.  Where  piles  are  used  in  the  foundations  the  soft  silt  or  mud  shall  be 
excavated  to  a  stratum  of  sufficient  firmness  to  give  lateral  support  and 
for  important  structures  such  as  piers  for  movable  bridges,  arches  and  high 
abutments  the  space  around  and  between  the  piles  shall  be  filled  with 
riprap  or  gravel  as  indicated  on  the  plans  or  as  may  be  required  by  the 
engineer.  When  not  indicated  or  specified,  the  cost  of  riprap  shall  be 
paid  by  the  company.  Piles  shall  not  be  used  for  any  important  work, 
even  when  called  for  on  the  plans,  unless  there  can  be  obtained  a  penetra- 
tion of  at  least  12  feet  in  firm  material  or  30  feet  in  soft  ground,  or  unless 
their  use  is  authorized  by  the  engineer  after  the  conditions  are  fully  known, 
in  which  case  he  shall  determine  the  number  required  in  addition  to  those 
shown  on  the  plans  and  the  location  of  the  brace  or  batter  piles  necessary 
for  lateral  support.  Piles  shall  be  located  accurately  in  the  positions 
indicated  and  cut  off  at  the  required  elevation.  They  may  be  driven 
either  by  gravity  or  steam-hammer.s,  but  shall  have  their  butts  protected 
with  metal  bands,  cushions  or  other  means  for  preventing  damage,  and 
shall  be  handled  and  driven  in  a  manner  that  will  insure  them  against 
injury.  Where  the  strata  are  of  such  a  nature  that  driving  is  liable  to 
injure  the  piles  they  may  be  jetted  down  to  solid  ground.  Before  any 
piles  which  are  to  remain  in  the  completed  structure  are  ordered  or  driven 


ART.  38  SPECIFICATIONS  1  15 

the  contractor  shall  determine  the  length  required  by  driving  a  sufficient 
number  of  test  piles  for  this  purpose.  In  case  he  fails  to  do  this,  piles 
ordered  by  him  of  insufficient  length  for  proper  driving  shall  be  at  his  risk. 

133.  Timber  piles  shall  be  of  sound  longleaf  yellow  pine,  Douglas  fir, 
cypress  or  white  oak,  butt  cut  above  the  ground  swell,  from  sound  trees 
when  the  sap  is  down,  close  grained  and  solid,  free  from  injurious  ring 
shakes,  large,  unsound  or  loose  knots,  or  other  defects  which  may  materi- 
ally affect  their  strength  or  durability.     They  shall  have  a  uniform  taper 
from  butt  to  tip,  be  free  from  short  bends,  and  a  line  drawn  from  the  center 
of  the  butt  to  the  center  of  the  tip  shall  lie  wholly  within  the  body  of  the 
pile.     They  shall  be  peeled  soon  after  cutting,  and  all  knots  trimmed  close 
to  the  body  of  the  pile.     Unless  otherwise  indicated  on  the  plans,  the  mini- 
mum diameter  at  the  tip  shall  be  9  inches  for  lengths  up  to  30  feet,  8  inches 
for  lengths  over  30  feet  but  not  exceeding  50  feet,  and  7  inches  for  lengths 
over  50  feet.     The  minimum  diameter  at  one  -quarter  length  from  the  butt 
shall  be  12  inches  and  the  maximum  diameter  at  the  butt  20  inches. 
When  treated  piles  are  required  in  water  infested  with  wood  borers  the 
treatment  shall  be  with  dead  oil  of  coal  tar  or  other  acceptable  process  to 
the  extent  of  20  pounds  per  cubic  foot  unless  otherwise  specified. 

134.  When  driven  through  hard  ground  they  shall  be  shod  with  steel 
points  of  approved  design.     They  shall  go  to  rock  or  to  practical  refusal 
which  is  here  understood  to  mean  driven  to  such  depth  that  the  last 
five  blows  of  a  3000-pound  hammer  freely  falling  15  feet  upon  the  solid 
unbroomed  head  of  a  pile  shall  not  produce  an  average  penetration  greater 
than  one-half  inch  for  each  blow.     For  other  weights  of  drop-hammers 
falling  from  12  to  15  feet  and  for  steam-hammers,  the  penetration  for 
practical  refusal  as  above  defined  may  be  determined  from  the  following 
formulas: 

(a)  Gravity  hammers: 

5  =  W/77/3oooo  —  i.o;  average  for  each  of  last  five  blows 

(b)  Steam-hammers: 

s=  WH/soooo—o.i;  average  for  each  of  last  twenty  blows 
where  5  =  penetration  in  inches;  W=  weight  of  the  falling  hammer  in 
pounds;  H  =  height  of  the  fall  in  feet.  In  case  the  above  refusal  cannot 
be  obtained  without  injury  to  the  pile  or  on  account  of  the  impracticable 
lengths  required,  the  number  indicated  in  the  plans  shall  be  increased 
until  the  maximum  load  coming  on  any  pile  shall  not  exceed  that  deter- 
mined from  the  formulas: 

(a)  For  railway  bridges,  all  arches  and  movable  spans 

i.o6WH  e  i.o6WH  , 

P  =  —        —  for  gravity  hammer  ;  P  =  —         -  for  steam-hammer 

5+1 


(b)  For  other  structures  the  above  loads  may  be  increased  25  percent. 


CHAPTER  IV 
CONCRETE  PILES 

ARTICLE  39.     INTRODUCTION  AND  CLASSIFICATION 

Being  impressed  by  the  very  short  life  of  timber  piles  when 
their  upper  portions  are  alternately  wet  and  dry,  as  in  pile 
trestle  bridges,  the  increasing  cost  of  timber,  and  the  decreasing 
cost  of  cement,  A.  A.  RAYMOND  was  led  to  consider  the  design  and 
construction  of  concrete  piles.  He  first  used  such  piles  in  1901 
in  a  building  foundation  in  Chicago. 

In  1897,  HENNEBIQUE  introduced  the  reinforced-concrete 
pile  in  Europe,  and  in  1904  it  was  first  used  in  America.  Within 
the  first  decade  of  this  century,  a  number  of  other  forms  were 
developed,  differing  in  methods  of  construction,  some  of  them 
being  patented  by  the  inventors,  while  others  were  designed  by 
engineers,  without  the  use  of  patented  material,  form,  or 
arrangement. 

Concrete  piles  may  be  divided  into  two  general  classes:  The 
first  class  comprises  those  which  are  molded  to  a  regular  form, 
and  after  curing,  are  handled  and  driven  like  timber  piles;  while 
the  second  class  includes  those  formed  in  place  either  with  or 
without  the  use  of  casings  which  remain  until  destroyed  by 
corrosion.  The  former  may  be  called  pre-molded  piles  and  the 
latter,  cast-in-place  piles.  Pre-molded  piles  were  first  developed 
in  Europe  and  practice  in  that  country  has  practically  confined 
the  use  of  concrete  piles  to  that  class.  The  cast-in-place  piles 
were  invented  in  America  and  on  that  account  came  into 
considerable  use  before  the  advantageous  features  of  pre-molded 
piles  came  to  be  generally  recognized. 

Pre-molded  piles  are  always  reinforced  with  steel  bars  or 
rods  in  combination  with  lateral  reinforcement  in  the  form  of 
wire  hoops  or  spiral  wrapping.  They  are  square,  hexagonal, 

116 


ART.  39  INTRODUCTION  AND   CLASSIFICATION  1 17 

octagonal,  or  circular  in  cross-section,  the  corners  of  square  piles 
being  chamfered,  however.  Piles  with  a  circular  cross-section 
generally  have  no  taper,  while  the  others  are  usually  tapered 
from  butt  to  tip. 

This  class  includes  several  distinct  types.  The  Chenoweth 
pile  is  formed  by  rolling  it  in  a  machine  especially  designed 
for  the  purpose,  the  reinforcement  being  arranged,  so  as  to 
show  a  spiral  form  in  cross-section.  The  corrugated  pile  is 
octagonal  in  section  but  with  a  semi-circular  corrugation  on  each 
face  intended  to  increase  the  surface  for  frictional  resistance, 
and  with  a  hole  along  its  axis. 

The  Cummings  pile  is  distinguished  mainly  by  the  character 
and  arrangement  of  the  reinforcement,  which  is  electrically 
welded  and  handled  as  a  unit.  In  some  cases,  annular  grooves 
are  molded  on  the  surface.  The  preceding  types  are  patented, 
but  most  of  the  pre-molded  piles  are  unpatented  and  simple  in 
construction,  as  illustrated  in  Art.  41. 

Cast-in-place  piles  are  usually  not  reinforced,  although 
this  feature  may  be  added.  The  type  in  most  extensive  use  at 
present  (1914)  is  the  Raymond  pile.  It  is  made  by  first  driving 
a  steel  collapsible  core  with  a  sheet-iron  form,  which  remains  in 
place  after  the  core  is  withdrawn,  and  is  then  filled  with  con- 
crete. The  simplex  pile  is  made  by  driving  a  steel  pipe  with 
movoble  point  into  the  earth  and  filling  the  hole  with  concrete, 
as  the  pipe  is  gradually  withdrawn.  The  pedestal  pile  differs 
from  the  simplex  in  having  an  enlarged  foot  formed  by  means 
of  a  plunger  which  forces  the  concrete  to  make  and  fill  an  en- 
largement in  the  hole  during  the  withdrawal  of  the  pipe  for 
several  feet  from  the  bottom.  In  the  peerless  sectional  pile, 
sectional  concrete  casings  are  driven  into  place  and  afterward 
filled  with  concrete.  Practically  all  cast-in-place  piles  are 
patented.  Their  construction  is  described  and  illustrated  in 
Art.  45. 

In  the  bulkhead  construction  for  the  new  port  at  San  Diego, 
Cal.,  a  combination  concrete  and  timber  pile  was  used.  A 
wooden  pile,  14  inches  in  diameter  was  driven  into  the  harbor 
bottom,  a  hollow  concrete  cylinder  cast  on  shore,  was  then  driven 


Il8  CONCRETE  PILES  CHAP.  IV 

over  the  pile  to  a  depth  of  4  or  5  feet  below  the  bottom  of  the 
harbor,  and  rilled  with  concrete.  For  additional  details  and 
illustrations  see  Engineering  News,  vol.  69,  page  498,  March 


ART.  40.  RELATIVE  ADVANTAGES 

Timber  piles  in  ordinary  foundations  must  be  cut  off  below 
the  permanent  ground-water  level,  which  often  involves  the 
cost  of  extra  excavation.  When  the  water-level  is  lowered  by 
changes  in  the  drainage  system  due  to  the  construction  of 
subways,  the  lowering  of  sewers,  or  for  other  causes,  the 
piles  become  liable  to  rot  and  may  involve  expensive  changes 
in  the  foundation. 

The  durability  of  concrete  piles  is  independent  of  the  ground- 
water  level.  Concrete  piles  have  a  material  advantage  on 
account  of  their  greater  bearing  capacity,  due  to  their  larger 
size,  thus  permitting  a  material  reduction  in  the  number 
required  to  support  a  given  structure.  The  bearing  capacity 
may  be  further  enlarged  under  some  conditions  by  increasing 
the  taper.  Roughly,  the  loading  of  timber  piles  is  restricted 
by  engineers  within  a  range  of  10  to  20  tons,  while  concrete 
piles  may  be  loaded  from  20  to  50  tons. 

On  the  other  hand,  a  concrete  pile  costs  considerably  more 
than  a  timber  pile.  Since  the  life  of  concrete  piles  is  not 
dependent  upon  the  ground-water  level,  their  use  not  only 
avoids  extra  excavation,  but  as  a  direct  consequence,  a  saving 
in  the  masonry  walls  or  footings.  Most  frequently,  this  is  the 
largest  factor  in  saving  afforded  by  the  substitution  of  concrete 
piles,  provided  the  tops  of  the  concrete  piles  can  be  placed  more 
than  3  feet  higher  than  for  timber  piles.  They  may  also  be 
readily  bonded  into  the  grillage  or  capping  of  concrete,  and  will 
act  together  as  a  monolith,  provided  reinforcement  is  used  in 
the  piles.  Less  excavation  and  smaller  footings  imply  a  reduc- 
tion in  the  time  of  construction. 

When  pre-molded  piles  are  employed,  they  require  more 
time  and  care  in  handling  than  timber  piles,  on  account  of 


ART.  40  RELATIVE   ADVANTAGES  1 19 

their  greater  weight,  and  their  relatively  lower  flexural  strength. 
In  general,  concrete  piles  cannot  be  driven  as  rapidly  as  timber 
piles,  but  the  number  required  may  be  sufficiently  smaller  to 
affect  a  saving  in  time,  as  well  as  in  cost.  As  sand,  stone  and 
cement  are  generally  available,  there  is  less  probability  of  delay, 
occasioned  by  waiting  for  the  arrival  of  piles  at  the  site.  Some- 
times the  value  of  the  time  saved  pays  for  a  considerable  part 
of  the  piles.  In  some  track-elevation  work  in  cities,  the  use  of 
concrete  piles  for  the  foundations  of  retaining  walls  has  made  a 
large  saving  by  reducing  the  required  width  of  new  right-of-way 
at  the  excessive  rates  which  had  to  be  paid. 

In  emergencies,  concrete  piles  have  sometimes  shown  unusual 
flexural  strength.  In  one  case,  a  single  pile  acting  as  a  canti- 
lever, 32  feet  long,  successfully  withstood  the  test,  when  a 
g-inch  hawser  was  attached  to  its  upper  end  to  pull  a  steamer 
of  4800  tons  displacement  to  the  unfinished  pier  against  a  rapidly 
running  tide.  At  another  time,  a  steamer  ran  into  the  pier  by 
accident,  and  broke  off  a  number  of  pine  piles,  but  none  of  the 
concrete  piles.  It  may  be  added,  that  concrete  piles  may  be 
placed  in  some  filled  material  through  which  it  is  impossible  to 
drive  timber  piles  without  injury.  Strict  economy  requires 
adequate  exploration  of  the  soil  to  be  made  to  determine  the 
proper  lengths  of  piles.  Failure  to  do  so,  leads  to  waste 
of  timber  by  excessive  cut-offs,  but  with  concrete  piles,  the 
waste  of  time  may  be  even  more  serious  than  that  of  mate- 
rial and  labor. 

Inspectors  realize  how  difficult  it  is  often  to  find  a  fair  per- 
centage of  timber  piles  which  fill  the  demands  of  the  specifica- 
tions in  all  particulars,  regarding  diameter  of  butt,  diameter  of 
tip,  straightness  or  other  qualities,  especially  when  the  required 
length  exceeds  50  feet.  On  the  other  hand,  with  reasonable 
care,  every  concrete  pile  can  be  made  to  comply  fully  with  the 
specifications.  Moreover,  the  strength  of  concrete  piles 
improves  with  age. 

As  the  forest  resources  are  being  reduced,  it  becomes  increas- 
ingly difficult  to  get  the  larger  sizes  of  timber  piles,  while  at  the 
same  time,  the  quality  of  the  wood  becomes  poorer.  Although 


1 20  CONCRETE  PILES  CHAP.  IV 

the  safe  allowable  compression  for  concrete  is  less  than  for  wood 
on  the  ends  of  the  fibers,  the  loading  of  a  pile  depends  more 
frequently  on  the  supporting  capacity  of  the  earth,  than  on  the 
strength  of  the  pile. 

There  are  minor  advantages  that  can  only  be  adequately 
considered  in  the  detailed  design  and  estimate  of  cost  for  a 
given  structure.  Any  decrease  in  the  masonry  of  walls  or 
footings  has  a  secondary  influence  on  the  cost  of  the  foundation 
by  reducing  the  weight  to  be  supported,  provided  this  is  not 
wholly  off-set  by  the  increased  weight  of  concrete  piles.  Simi- 
larly a  reduction  in  excavation  may  lessen  the  amount  of 
sheeting,  shoring,  pumping,  back-filling,  etc.  These  items  are 
often  difficult  to  estimate  and  hence  contractors,  as  well  as 
engineers,  prefer  to  eliminate  them,  if  possible. 

In  the  following  example,  the  cost  with  concrete  piles  is 
greater  than  for  concrete  piers  in  shafts  sunk  to  rock,  but  the 
piles  had  to  be  adopted  since  a  stratum  of  fine  water-bearing 
sand  was  discovered  when  an  unsuccessful  attempt  was  made  to 
put  down  the  first  shaft  of  bent  15.  The  -statement  below 
gives  a  comparative  estimate  of  cost  of  foundations  for  tower 
No.  15-16  of  the  Municipal  Bridge  Approach  at  St.  Louis. 

Concrete  Piers  Concrete  Piles 

Concrete,  cu.  yds 302. 3  ©$5. 70    $1725         127. 8  ©$5. 70      $728 

Excavation,  cu.  yds. .  .325.5  @  1.75  570  216.4©  0.60  130 
Concrete  piles,  lin.  ft 1550  @  i.io  1705 


Total  for  6  piers $2295  $2563 

As  indicated  on  the  boring  sheet,  the  average  depth  of  rock 
above  the  ground  surface  was  about  31  feet.  The  yardage 
cost  of  concrete  includes  cost  of  forms;  and  that  of  excavation 
includes  sheeting,  shoring  and  pumping.  The  reinforced 
concrete  piles  were  driven  through  strata  of  filled  ground,  shore 
sand,  blue  sandy  clay,  coarse  sand  and  gravel,  and  river  sand 
to  rock. 

In  salt  water  infested  by  the  teredo  or  limnoria,  the  timber 
pile  requires  expensive  protection  either  by  chemical  treatment 


ART.  40  .     RELATIVE   ADVANTAGES  121 

(Art.  21),  or  by  mechnical  means  (Art.  22).     The  concrete  pile 
is  wholly  free  from  the  ravages  of  these  borers. 

The  following  example  illustrates  the  method  adopted  to 
determine  the  comparative  cost  of  foundations  designed  for  the 
use  of  timber  and  concrete  piles  respectively.  On  account  of 
increase  in  traffic  and  live  loads,  causing  settlement  of  the  foot- 
ings supported  by  piles,  and  requiring  an  additional  track  later, 
substantial  reconstruction  became  necessary  for  the  viaduct 
foundations  of  the  Norfolk  and  Western  Railway  approach 
viaduct  at  Kenova,  W.  Va.  Two  designs  were  made  to 
determine  which  was  the  more  economical  to  construct.  In 
one  plan  three  rows  of  four  creosoted  piles  each  with  four  caps 
were  placed  under  concrete  footings,  while  in  the  other  plan, 
concrete  piles  were  used  under  each  footing,  three  piles  being 
placed  in  each  of  the  two  outer  rows  and  two  in  the  middle  row. 
The  comparative  estimates  of  the  average  cost  of  each  footing 
were  as  follows: 

DESIGN  WITH  TIMBER  PILES 

31  cu.  yds.  excavation  @  50  cts $15.50 

22  cu.  yds.  portland  cement  concrete  @  $6.50 143.00 

348  ft.  B.  M.  creosoted  timber  @  $45.00 17.28 

240  ft.  creosoted  piles  @  56  cts 134.40 

55  Ibs.  iron  @  6  cts 3.30 


$31348 

DESIGN  WITH  CONCRETE  PILES 

20  cu.  yds.  excavation  @>  50  cts $10.00 

14  cu.  yds.  portland  cement  concrete  @  $6.50 91.00 

8  concrete  piles  @  $22.00 ; 176.00 


$277.00 
Estimated  saving  on  each  footing $36.48 

The  concrete  piles  were  20  feet  long,  20  inches  in  diameter  at 
the  head  and  6  inches  at  the  foot.  On  account  of  the  size  and 
taper  of  the  concrete  piles  a  smaller  number  could  be  used.  The 
reduced  amount  of  excavation  and  of  concrete  in  the  footings 
effected  the  balance  of  the  saving  in  cost.  The  size  of  the  con- 


122  CONCRETE   PILES  CHAP.  IV 

crete  cap  and  footing  was  in  both  cases  4  by  6  feet  on  top  and 
8  by  10  feet  on  the  bottom,  but  the  height  was  reduced  from  n 
to  6  feet. 

ART.  41.     UNPATENTED  PRE-MOLDED  PILES 

A  pre-molded  pile  is  a  reinforced  concrete  pile  which  is  molded 
to  a  regular  form  and  after  curing  and  seasoning  is  handled  and 
driven  like  a  timber  pile.  In  order  to  indicate  the  principal 
variations  in  form  and  reinforcement  which  have  been  developed 
by  different  designers  of  pre-molded  concrete  piles,  brief  descrip- 
tions are  given  either  of  standard  designs  or  of  those  adopted  for 
the  foundations  of  particular  structures. 

The  bridge  department  of  the  Chicago,  Burlington  &  Quincy 
Railroad  was  a  pioneer  in  the  design  and  construction  of  low 
reinforced-concrete  pile  trestles  for  steam  railroads.  In  con- 
nection with  the  thorough  studies  and  tests  made  for  this 
purpose,  an  unpatented  type  of  pre-molded  pile  was  developed 
in  1905  which  together  with  the  Chenoweth  rolled  pile  (Fig.  41  b), 
has  been  extensively  used  in  construction  by  that  railroad.  The 
piles  used  in  the  first  of  these  bridges  are  16  inches  square  at  the 
butt,  have  a  4-inch  chamfer  at  each  corner,  a  taper  of  4  inches  in 
30  feet  on  each  face,  and  are  pointed  at  the  tip.  The  rein- 
forcement consists  of  four  f -inch  square  corrugated  bars,  hooped 
with  No.  12  steel  wire,  wound  at  close  pitch  near  the  butt  and 
tip,  and  at  3-inch  pitch  over  the  greatest  part  of  the  length 
of  the  pile. 

Since  the  cost  of  making  the  reinforcement  units  was  one  of 
the  principal  items,  experiments  were  made  to  reduce  it  by  mold- 
ing a  pile  without  taper,  and  using  a  wire  netting  which  could 
then  be  simply  folded  into  a  square  prismatic  form  and  wired 
together  at  the  lap,  thus  greatly  lessening  the  labor  involved. 
The  cost  of  forms  was  thereby  also  materially  reduced.  Fig. 
410  shows  the  details  of  the  form  and  reinforcement  of  this  later 
design.  It  will  be  observed  that  the  corners  of  the  pile  are 
rounded  and  that  the  loi)gitudinal  bars  are  wired  to  the  fabric 
at  its  corners.  At  the  point,  the  transverse  wires  were  cut  and 


ART.  41 


UNPATENTED    PRE-MOLDED    PILES 


I23 


the  longitudinal  wires  brought  together  and  tied  securely  with 
small  wire. 

The  concrete  piles  driven  in  1909  in  the  foundations  of  eight 
of  the  piers  of  the  Erie  Railroad  viaduct  over  Penhorn  Creek  in 
Jersey  City,  have  the  re: 
markable  lengths  of  55  to  65 
feet.  They  are  square  in 
cross-section,  tapered  from 
1 6  inches  at  the  butt  to  8 
inches  at  the  tip,  and  have 
a  2-inch  hole-  through  the 
axis  from  end  to  end.  Each 
corner  is  reinforced  by  a 
single  f-inch  round  steel 
rod.  Especial  pains  were 
taken  to  design  them  so 
that  no  patented  features 
were  incorporated. 

Reinforced- concrete  piles 
were  designed  by  the  Penn- 
sylvania Lines  for  their  ex- 
tensive docks  at  Cleveland, 
0.,  and  which  were  con- 
structed by  the  Great  Lakes 
Dredge  and  Dock  Com- 
pany. They  are  octagonal 
in  shape,  without  taper, 
pointed  at  the  foot  and  have 
a  cast-iron  shoe  which  was 
made  an  integral  part  of  the 
pile.  As  indicated  in  Fig. 
4  id,  the  reinforcement  con- 
sists of  8  longitudinal  rods  securely  bound  together  at  regular 
intervals  throughout  the  body  of  the  pile  by  tie  rods.  They 
are  also  spirally  wrapped  for  short  distances  at  both  head  and 
foot.  The  dimensions  in  Fig.  4  id  refer  to  piles  30  to  40  feet  long, 
the  longitudinal  rods  being  i  inch  in  diameter,  while  the  ties  and 


k- 


FIG. 


FIG.  416. 


124 


CONCRETE   PILES 


CHAP.  IV 


wrapping  are  f  inch  in  diameter.  Over  3500  octagonal  piles 
were  used  on  the  dock  foundations  and  all  of  them  were  cast  in 
vertical  molds.  The  weight  of  the  largest  pile  is  6  tons. 

The  standard  design  of  the  Chicago,  Rock  Island  &  Pacific 
Railway  adopted  in  1910  is  illustrated  in  Fig.  416.     The  form 


FIGS.  4ic  and  d. 

is  octagonal,  without  taper  and  pointed  at  the  foot.  The  rein- 
forcement occupies  a  cylindrical  form  in  the  body  of  the  pile, 
and  consists  of  6  longitudinal  corrugated  bars  and  spiral  wrap- 
pings of  wire  with  a  small  pitch,  which  is  slightly  modified  near 
the  head  and  foot.  The  bars  extend  to  the  point  but  not  quite 
to  the  upper  end  and  are  wired  to  the  helical  reinforcement  at 
intervals  not  exceeding  12  inches. 


ART.  41 


UNPATENTED    PRE-MOLDED   PILES 


125 


A  similar  design  was  adopted  for  some  pile  foundations  in  the 
approaches  of  the  Municipal  bridge  at  St.  Louis,  Mo.,  in  1911. 
The  least  diameter  is  also  14  inches  and  the  reinforcement  con- 
sists of  six  f -inch  round  rods,  and  a  helical  winding  with  No.  9 
wire  on  a  pitch  of  4  inches,  reduced  to  i  inch  for  about  18  inches 
at  the  head  of  the  pile. 


Concrete  Pile  Devotion  Section  D-D 

FIG.  4ie. — Concrete  Pile  and  Forms. 

The  pre-molded  piles  designed  for  the  Government  Pier  at 
Halifax,  N.  S.,  are  24  inches  square  in  section  with  the  corners 
slightly  chamfered.  The  8  reinforcing  rods  are  i  inch  in  diame- 
ter for  piles  under  60  feet  in  length,  i  J  inches  for  lengths  of  60 
to  70  feet,  and  i  \  inches  for  lengths  over  70  feet.  In  addition 
to  these  rods  which  extend  from  the  pyramidal  point  to  3  feet 
above  the  head  so  as  to  bond  into  the  superstructure,  four  rods  8 
feet  long  extend  from  the  point  upward  about  midway  between 


126  CONCRETE   PILES  CHAP.  IV 

the  axis  and  the  full-length  corner  rods.  Helical  wrapping  with 
|-inch  wire  and  a  pitch  of  2  inches  is  used  for  a  distance  of  5^ 
feet  above  the  point.  Beyond  that  the  wire  hoops  are  spaced 
12  inches  apart  except  at  the  head  where  the  spaces  are  reduced 
to  9  and  6  inches  respectively. 

The  reinforced-concrete  piles  used  in  1906-07  in  the  founda- 
tions of  the  steamship  terminal  of  the  Atlanta,  Birmingham  and 
Atlantic  Railway  at  Brunswick,  Ga.?  were  tapered  for  a  length  of 
only  10  feet  from  the  tip.  Their  length  ranges  from  30  to  51 
feet  and  their  weight  from  3  to  5  tons  each.  They  are  16  inches 
square  from  the  shoulders  to  a  section  10  feet  from  the  tip  and 
8  inches  at  the  tip.  Above  the  shoulders,  they  have  a  projecting 
tenon,  8X16  inches  and  16  inches  long  to  permit  concrete  fillers 
to  be  placed  in  the  shoulders  to  increase  the  bearing  area  of  the 
packed  timber  beams  used  in  the  floor  of  the  pier.  The  rein- 
forcement consists  of  four  ij-inch  bars  placed  in  the  corners  of 
the  pile  and  tied  together  at  1 2-inch  intervals  by  J-inch  round 
steel  clips.  At  the  head  electric-welded  wire  fabric  is  placed 
for  a  length  of  4  feet  to  aid  in  withstanding  the  shock  from 
hammering.  A  i^-inch  jet  pipe  was  cast  into  the  lower  part  of 
the  pile  for  subsequent  use  in  sinking. 

The  piles  used  in  1907  at  the  Charles  town  Navy  Yard  were 
noteworthy  on  account  of  their  size  and  weight.  In  design, 
they  are  similar  to  those  described  in  the  preceding  paragraph. 
They  are  55  feet  long  and  18  inches  square  to  within  8  feet  of  the 
tip  and  then  tapered  off  to  1 2  inches  square.  The  reinforcement 
consists  of  four  ij-inch  twisted  bars  and  two  f -inch  bars.  The 
larger  bars  are  placed  in  the  comers  of  the  pile  2\  inches  from 
the  surface,  and  the  smaller  ones  are  placed  between  the  others 
and  on  a  line  across  the  pier  transversely.  A  2-inch  pipe  22  feet 
long  was  cast  in  the  pile  for  use  as  a  water-jet.  As  the  weight 
of  a  pile  is  10  tons,  a  bridle  which  picked  up  a  pile  at  two  points, 
1 8  feet  apart,  was  employed  in  lifting  them. 

Pre-molded  round  piles,  12  inches  in  diameter  but  having  a 
bulb-shaped  foot  30  inches  in  diameter  and  24  inches  high,  were 
used  on  some  new  work  for  the  reconstruction  of  the  '  old  steel 
pier'  at  Atlantic  City,  into  a  reinforced-concrete  pier.  The 


ART.  42 


PATENTED   PRE-MOLDED   PILES 


I27 


longitudinal  reinforcement  consists  of  six  f -inch  bars,  and  these 
are  splayed  out  at  the  bottom  to  reinforce  the  foot,  which 
is  intended  to  increase  the  bearing  power  in  the  sand.  A 
2-inch  jet  pipe  was  cast  in  the  pile  and  extends  throughout 
its  full  length. 


ART.  42.     PATENTED  PRE-MOLDED  PILES 

The  corrugated  pile  is  hexagonal  or  octagonal  in  cross-section 
with  grooves  approximately  semi-cylindrical  on  each  face,  has 
a  round  hole  along  the  axis,  both  pile  and  hole  being  tapered  from 
butt  to  tip,  and  is  reinforced  with  electrically  welded  wire  fabric 
(Fig.  420).  The  hole  or  central  bore  is  used  to  permit  a  water- 
jet  to  pass  through  it,  and  it  is  tapered  to  increase  the  section 


-  Wire  Mesh  • 

'—-Reinforcing 
Bars- 


i  '*iy  ^Reinforcement 


FIG.  42a. — Section  of  Corru- 
gated Pile. 


End- Cross  Section 
for  All  Piles. 


Middle  Cross  Section 
for  Long  Piles. 


FIG.  426. — Sections  of  Chenoweth  Pile. 


area  of  concrete  at  the  tip  and  to  permit  the  plug  used  to  cast 
the  hole  to  be  easily  withdrawn.  The  object  of  the  corruga- 
tions is  to  increase  the  pile  surface  for  skin  friction,  and  to  fur- 
nish convenient  outlets  for  the  escaping  water  from  the  jet, 
thus  reducing  the  friction  during  the  operation  of  sinking. 
They  are  not  extended,  however,  along  the  head  or  tip,  to  avoid 
reducing  the  full  section  area  of  both  parts.  When  the  piles  are 
intended  to  project  above  the  ground  level,  the  corrugations  are 
designed  not  to  extend  above  it. 

The  Chenoweth  concrete  pile  is  a  rolled  pile.  The  machine 
used  for  this  purpose  has  a  moving  platform,  a  number  of  rolls 
and  mechanism  to  turn  the  tubular  mandrel,  about  which  the 
pile  is  formed.  The  reinforcement  consists  of  a  number  of  lon- 
gitudinal corrugated  bars,  wired  to  transverse  strips  of  wire 


128  CONCRETE   PILES  CHAP.  IV 

mesh.  This  reinforcement  is  laid  out  on  the  platform  and  the 
ends  of  the  wire  mesh  attached  by  wire  clips  to  the  key  ways  of 
the  mandrel;  the  concrete  is  property  spread  over  it  and  then  by 
simultaneously  turning  the  mandrel  and  moving  the  platform, 
the  pile  'is  coiled  and  rolled  into  a  cylindrical  form  which  is 
compacted  and  shaped  by  means  of  the  adjustable  rollers.  At 
the  same  time,  the  pile  is  wound  by  wire  at  about  6-inch  inter- 
vals during  the  entire  process  of  rolling.  After  fastening  the 
ends  of  these  wires,  the  central  tube  is  withdrawn,  and  the  pile 
is  removed  to  the  drying  table.  A  concrete  point  shaped  like 
the  frustum  of  a  cone  is  constructed  around  the  projecting 
reinforcing  bars  with  the  aid  of  a  suitable  form,  and  the  head  is 
perfected  in  a  similar  manner.  The  wire  netting  in  the  finished 
pile  is  located  in  a  spiral  surface,  as  indicated  in  the  cross-section 
shown  in  Fig.  426,  while  the  longitudinal  bars  are  equidistant 
near  the  surface  of  the  pile.  In  making  these  piles,  a  very  dry 
mixture  has  to  be  used;  otherwise,  the  cement  will  be  squeezed 
out  with  the  water  in  rolling.  If  the  mixture  is  too  wet,  the 
piles  will  also  lose  their  shape  and  become  oval  on  the  drying 
table.  On  some  railroads,  it  is  the  practice  to  omit  pointing  the 
rolled  piles,  leaving  the  tip,  just  as  it  comes  from  the  rolls. 

The  largest  pile  of  this  type  employed  prior  to  1913,  was  used 
in  a  coal  dock  at  Havana,  the  length  being  76  feet,  diameter  18 
inches,  and  weight  12  tons.  At  the  end  of  the  dock,  the  piles 
are  unsupported  for  a  length  of  40  feet  and  their  penetration 
extends  2  feet  into  the  coral  rock.  Piles  50  feet  long  and  only 
12  inches  in  diameter  have  been  successfully  handled. 
Piles  of  the  same  length  but  14  inches  in  diameter  and 
weighing  3^  tons  have  been  hauled  four  miles  to  the  site  of  the 
foundation. 

The  reinforcement  of  the  Cummings  concrete  pile  is  illus- 
trated in  Fig.  420.  Four  of  the  longitudinal  bars  do  not  extend 
the  full  length  of  the  pile.  The  other  four  are  welded  together 
at  the  point,  and  welded  to  a  conical  sheet-metal  point  protector 
or  shoe.  They  are  also  bent  over  at  the  head  and  welded 
together  in  pairs.  The  longitudinal  rods  are  held  in  position,  at 
intervals  of  approximately  5  feet,  by  flat  rings  of  |-mch  metal 


ART.  42 


PATENTED   PRE-MOLDED   PILES 


129 


K 14'- 


with  notches  cut  in  the  circumference  to  receive  the  rods.  The 
body  of  the  pile  has  a  helical  wrapping  of  wire  to  perform  the 
function  of  hooping  and  to  aid  in  resisting  diagonal  stresses. 

At  the  head  there  is  also  a  series  of  horizontal  bands  closely 
spaced  to  give  special  lateral  support  to  the  concrete  under  the 
driving  shock  and  each  of 
the  upper  four  of  these 
contains  a  horizontal  spiral 
as  shown  in  the  sketch 
plan.  Sometimes  seven 
are  used  in  large  piles. 
This  arrangement  for  re- 
inforcing the  pile  head  has 
proven  to  be  very  resistant 
to  the  impact  of  the  pile- 
driver  hammer.  It  is 
claimed,  that  in  driving 
thousands  of  piles  with 
this  resilient  head,  that  in 
no  case  was  the  head  of  the 
pile  broken. 

Fig.  420  shows  the  ta- 
pered form  which  is  always 
made  with  an  octagonal 
cross-section  and  a  tip  9 
inches  in  diameter;  the 
diameter  of  the  butt  de- 
pending upon  the  length 
of  the  pile  so  as  to  preserve 

a  constant  taper  of  2  inches  in  10  feet  in  the  standard  designs. 
When  a  pile  of  uniform  section  is  used,  the  form  of  the 
cross-section  is  circular.  Sometimes  both  the  tapered  and  un- 
tapered  piles  are  molded  with  annular  grooves  to  increase  the 
frictional  resistance. 

The  ordinary  form  of  the  Hennebique  pile  is  usually  con- 
structed as  a  square  pile  without  taper,  with  the  reinforcing 
bars  near  the  four  edges  which  are  slightly  beveled  and  tied 

9 


i 

Shoe 

FIG.  42C. — Reinforcement  of  Cummings 
Concrete  Pile. 


130  CONCRETE   PILES  CHAP.  IV 

together  by  wire  collars  or  binders  at  short  intervals.  The 
standard  form  has  a  cast-steel  shoe  at  the  foot  forming  an  inte- 
gral part  of  the  pile.  To  support  a  reinforced-concrete  quay,  at 
Key  West,  piles  16  and  20  inches  square  and  from  25  to  60  feet 
long  were  driven  through  marl  and  sand  into  the  coral  rock ;  all 
of  them  being  provided  with  metal  shoes.  The  longitudinal 
reinforcement  consisted  of  four  rods  i|  inches  in  diameter,  with 
extra  rods  in  the  middle  third  of  the  longest  piles.  The  J-inch 
wire  collars  were  spaced  12  inches  apart  in  the  body  of  the  pile, 
4  inches  in  the  head,  6  and  3  inches  in  the  tip.  A  pile  of  this 
kind,  which  was  constructed  as  a  hollow  pile  to  reduce  its 
weight,  and  was  filled  with  concrete  when  in  place,  is  described 
in  Art.  47. 

Further  details  as  to  sizes  of  piles,  sizes  and  disposition  of 
reinforcement,  and  methods  of  construction  may  be  found  in 
the  elaborately  illustrated  catalogues  which  are  published  by 
the  construction  companies. 

ART.  43.     FORM  AND  CONSTRUCTION 

The  prevailing  form  of  cross-section  for  pre-molded  piles  is 
octagonal.  Practically  all  of  those  with  square  sections 
approximate  toward  the  octagonal  form  in  that  their  edges  are 
beveled  to  a  width  of  2  or  3  inches,  although  occasionally  they 
are  merely  rounded  (see  Fig.  410).  The  circular  cross-section  is 
used  but  seldom,  in  which  case  the  piles  must  be  cast  in  a  vertical 
position.  The  diameter  varies  from  10  to  25  inches  but  it  is 
rarely  below  12  or  above  18  inches.  The  length  varies  from  8 
to  76  feet,  but  it  is  questionable  whether  any  length  less  than 
15  feet  should  be  employed  in  any  pile  foundation.  In  most 
cases  the  length  ranges  from  20  to  40  feet.  The  longest  piles 
are  used  in  dock  construction  where  the  piles  are  located  in 
deep  water. 

It  would  be  difficult  to  say  whether  more  pre-molded  piles  are 
constructed  with  taper  than  without  it,  for  both  forms  are  in 
extensive  use.  A  number  of  railroads  have  adopted  the  straight 
or  untapered  pile  as  standard,  and  in  a  considerable  number 
of  important  works,  each  one  requiring  thousands  of  piles,  half 


ART.  43  FORM  AND   CONSTRUCTION  131 

of  them  use  the  form  with  uniform  cross-section.  This  form 
should  always  be  used  when  conditions  require  the  pile  to  act 
chiefly  as  a  column. 

The  tendency  is  to  use  a  decidedly  smaller  taper  in  pre-molded 
piles  than  that  for  cast-in-place  piles.  It  may  be  stated  that 
except  for  very  short  piles  in  the  foundations  of  buildings,  the 
taper  does  not  exceed  i  inch  in  4  feet,  is  frequently  i  inch  in 
5  feet  and  sometimes  as  low  as  i  inch  in  7.5  feet.  The  influence 
of  taper  on  the  bearing  power  of  piles  is  discussed  in  Art.  53. 

As  indicated  in  Arts.  41  and  42,  pre-molded  piles  are  most 
frequently  designed  with  a  point  at  the  foot.  Its  length  often 
exceeds  but  is  sometimes  less  than  the  diameter.  Even  in 
tapered  piles  experience  has  shown  the  advantage  of  a  point. 
In  driving  piles  for  the  Kentucky  shore  pier  of  the  Kentucky 
and  Indiana  bridge  at  Louisville  in  1910  the  9-inch  tip  of  the 
pile  was  made  square  ended  to  insure  straight  driving.  But 
as  driving  through  the  hard  clay  proved  to  be  so  difficult 
the  last  batch  of  piles  for  the  pier  footing  was  provided 
with  pyramid  points,  which  increased  three-fold  the  number 
driven  per  day. 

In  some  experiments  reported  in  1908  made  by  THOMPSON 
and  Fox  with  tapered  piles  30^  feet  long  it  was  found  that  the 
8-inch  tip  required  less  time  to  drive  the  piles  than  9  or  lo-inch 
tips,  although  in  this  case  the  result  was  complicated  by  the 
effect  of  difference  in  taper.  The  use  of  metal  shoes  in  pre- 
molded  piles  is  referred  to  in  Arts.  41  and  42.  See  Fig.  4id 
for  an  illustration  of  one  form. 

Sometimes  the  foot  of  the  pile  has  been  enlarged  in  diameter 
in  order  to  increase  the  bearing  area  of  the  pile  in  the  lower 
stratum.  One  example  of  this  practice  is  found  in  the  1 6-inch 
reinforced  concrete  piles  for  the  Atlantic  City  boardwalk  built 
in  1908  which  were  formed  with  a  base  26  inches  in  diameter. 
See  also  Art.  41. 

It  is  customary  in  good  practice  to  fabricate  the  reinforce- 
ment as  a  unit  so  that  it  can  be  easily  handled  and  placed 
quickly  in  the  form  when  the  process  of  casting  is  under  way. 
The  reinforcement  unit  is  held  in  accurate  position  in  the 


132  CONCRETE  PILES  CHAP.  IV 

forms  by  suitable  hangers  and  separators,  so  that  the  con- 
ditions assumed  in  designing  the  pile  shall  be  realized  in  its 
construction. 

If  the  pile  is  to  have  a  hole  in  the  center  for  the  insertion  of 
a  jet  pipe  to  be  used  in  sinking,  which  is  more  economical  than 
to  cast  a  jet  pipe  in  the  pile,  either  a  tapered  wooden  core  may 
be  used,  or  preferably  a  collapsible  form;  or  a  tin  tube  may 
be  used  instead  and  left  in  the  pile.  The  objection  to  the  solid 
core  is  that  it  requires  occasional  turning  to  prevent  its  sticking 
to  the  concrete,  and  its  removal  later. 

The  composition  of  the  concrete  consists  of  i  part  portland 
cement,  2  parts  of  sand  and  4  parts  of  broken  stone  or  gravel. 
This  mixture  is  so  generally  employed  that  it  may  be  regarded  as 
standard.  Occasionally  it  is  modified  to  1-2-3.  In  large  hollow 
piles  the  molded  portion  may  have  a  composition  of  1-1.5-3 
and  a  leaner  mixture  like  1-3-5  or  1-3-6  employed  in  filling  the 
interior  after  they  are  in  place.  Usually  the  size  of  the  crushed 
stone  or  gravel  is  limited  to  f  inch.  Investigations  relating  to 
the  effect  of  sea  water  on  concrete  piles  have  not  resulted  in 
definite  conclusions.  Experience  has  shown  however  that  it  is 
important  to  make  as  dense  a  mixture  of  concrete  as  possible. 

At  first  piles  were  molded  in  forms  laid  horizontally  on  the 
ground  or  on  suitable  platforms.  Later  the  practice  of  molding 
piles  in  a  vertical  position  was  introduced  in  order  that  the  sur- 
face of  the  concrete  as  it  is  deposited  in  batches  shall  always  be 
perpendicular  to  the  direction  of  the  load  to  be  supported  by  the 
pile,  or  to  the  force  applied  by  the  hammer  in  driving.  When 
piles  are  molded  in  a  horizontal  position  special  care  should  be 
exercised  to  provide  an  unyielding  base  so  that  the  concrete  may 
not  be  subjected  to  flexural  stresses  while  in  the  process  of  set- 
ting. When  the  forms  are  vertical  special  precautions  must  be 
observed  in  tamping  or  puddling  the  concrete  to  eliminate  all 
voids.  In  one  case  where  361  piles  were  cast  vertically  in 
lengths  of  28  and  32  feet,  not  one  unsound  pile  was  found 
when  the  forms  were  removed.  Both  positions  of  the  molds 
have  been  used  on  large  constructions  where  adequate  equip- 
ment was  provided. 


ART.  43  FORM   AND   CONSTRUCTION  133 

With  horizontal  molds  the  sides  may  be  removed  in  from  24  to 
48  hours,  but  the  pile  is  allowed  to  rest  on  the  base  about  a  week 
longer  during  which  time  it  should  be  copiously  showered  with 
water  to  permit  complete  chemical  action  for  the  setting  of  the 
cement.  In  very  warm  weather  some  protection  from  the  sun 
may  be  required.  After  this  the  piles  may  be  removed  and  piled 
in  stacks  to  continue  seasoning,  using  an  equalizing  spreader  and 
bridle,  if  necessary  to  handle  them.  They  are  usually  allowed 
to  harden  for  at  least  three  weeks  more  before  they  are  driven. 
The  actual  time  to  be  allowed  in  each  case  depends  upon  the 
temperature  and  humidity  of  the  atmosphere,  while  the  age 
at  which  piles  may  be  placed  in  position  depends  also  upon  the 
character  of  the  ground  and  the  method  of  driving. 

The  hardening  of  the  concrete  may  be  materially  hastened  by 
curing  with  live  stream  under  cover.  The  piles  for  the  docks 
of  the  Pennsylvania  Lines  at  Cleveland  were  cast  vertically  in 
steel  forms.  The  pile  forms  were  then  closed  at  the  top  and 
placed  horizontally  on  a  floor  of  cross  timbers.  On  account  of 
the  late  season,  it  was  found  necessary  to  use  some  method  of 
artificial  seasoning  and  this  was  done  by  piling  up  the  newly 
filled  forms  and  covering  them  with  canvas.  A  steam-pipe  line 
provided  with  outlet  pipes  was  laid  to  discharge  steam  under 
the  cover,  and  to  maintain  a  temperature  of  about  80  degrees. 
The  forms  were  removed  in  from  12  to  18  hours,  thus  leaving 
the  concrete  piles  exposed  directly  to  the  steam  for  three  or  more 
days  afterward  until  they  were  set  sufficiently  to  be  handled  by 
a  derrick.  They  were  afterward  placed  by  derricks  in  the  stor- 
age yard  to  be  kept  at  least  30  days  before  driving. 

It  may  be  added  that  on  other  works  concrete  piles  have  been 
allowed  to  set  for  from  five  to  six  days  in  the  ordinary  manner 
and  then  gently  hoisted  to  the  curing  bed  with  25  or  30  stacked 
together  in  a  pile  with  wooden  spacing  blocks  between  them 
where  they  were  subjected  to  live  stream  for  two  or  three  days. 
They  were  then  driven  within  three  or  four  days  in  summer,  or 
within  ten  days  in  winter. 

As  soon  as  pre-molded  piles  are  driven  they  are  ready  to 
receive  their  load  from  the  superstructure  above. 


134  CONCRETE   PILES  CHAP.  IV 

ART.  44.     DESIGN  OF  PRE-MOLDED  PILES 

The  steel  reinforcement  of  a  concrete  pile  is  intended  to  resist 
the  stresses  due  to  handling  and  driving  the  pile,  and  to  the  load 
which  may  come  upon  it  in  its  final  position.  The  longitudinal 
bars  receive  their  greatest  stresses  when  the  pile  is  lifted  from 
a  horizontal  position.  Unless  the  pile  is  exceptionally  long  or 
heavy  it  is  often  picked  up  at  or  near  the  middle  in  going  to  or 
from  the  seasoning  yard,  or  a  line  may  be  attached  near  one  end 
to  drag  it  to  the  pile  driver.  In  the  former  case  the  pile  must  be 
strong  enough  to  resist  flexure  due  to  its  own  weight,  while  in 
the  latter  case  the  pile  must  not  only  sustain  its  own  weight  but 
also  shock  or  the  impact  due  to  meeting  obstacles,  which  sets  it 
into  active  vibration. 

When  so  handled  concrete  piles  rarely  fail  by  compression,  but 
cracks  develop  on  the  tension  side  which  sometimes  may  be  due 
to  the  rods  slipping.  Twisted  or  deformed  bars  are  preferable  to 
plain  rods  on  account  of  their  increased  bond  resistance.  Large 
cracks  may  endanger  the  permanency  of  the  reinforcement  by 
permitting  corrosion  to  occur.  It  is  also  important  that  uniform 
circumferential  spacing  of  the  bars  be  maintained  in  construc- 
tion as  any  side  of  an  octagonal  pile,  for  example,  may  become 
subject  to  tension. 

Some  designers  add  100  percent  to  the  weight  of  a  pile  to 
provide  for  the  shock  due  to  handling.  This  may  be  excessive 
in  cases  where  special  provision  is  made  for  proper  handling,  50 
percent  being  a  more  reasonable  allowance.  Very  long  piles 
have  extra  longitudinal  reinforcement  provided  in  the  middle 
third  or  half  of  the  length.  Sometimes  short  lengths  of  additional 
longitudinal  bars  are  inserted  in  the  head,  to  aid  in  resisting  the 
impact  due  to  the  hammer,  but  additional  hooping  is  more 
frequently  provided  for  this  purpose. 

The  lateral  reinforcement  is  of  two  distinct  types:  One  con- 
sists of  separate  wire  hoops  or  binders  either  approximately 
square  or  circular  in  shape,  and  spaced  at  intervals  which  vary 
more  or  less  along  the  length  of  the  pile;  the  other  consists  of  a 
continuous  spiral  wrapping  which  varies  in  pitch  at  the  head  and 


ART.  44  DESIGN   OF   PRE -MOLDED  PILES  135 

foot  of  the  pile.  It  is  primarily  intended  to  increase  the  resist- 
ance of  the  concrete  to  longitudinal  compression,  but  the  latter 
form  may  also  aid  in  resisting  diagonal  tension.  The  lateral 
reinforcement  is  equally  as  important  as  the  longitudinal. 

The  percentage  of  steel  in  the  section  area  of  the  pile  varies 
considerably  in  practice,  ranging  from  about  0.6  to  2.8  percent. 
In  the  pre-molded  piles  for  the  approach  of  the  Municipal  bridge 
at  St.  Louis,  the  total  reinforcement  amounted  to  i|  per- 
cent of  the  volume  of  the  pile.  Experiment  has  shown  that  hair 
cracks  develop  in  handling  when  the  reinforcement  is  less 
than  i  percent. 

The  section  area  of  the  head  must  be  sufficient  to  support  in 
direct  compression  the  safe  load  for  which  the  pile  is  designed. 
The  safe  unit-stresses  to  be  adopted  should  depend  upon  the 
quality  of  the  concrete,  the  percentage  of  reinforcement,  and  its 
arrangement,  as  well  as  the  character  of  the  loading.  If  the  pile 
is  tapered  the  critical  section  for  direct  compression  is  not  at  the 
butt  or  top  of  the  head  but  at  some  distance  below  the  surface  of 
the  ground. 

The  additional  allowance  for  hard  driving  in  any  case  is  pre- 
ferably made  by  a  direct  addition  to  the  section  area  or  by  adding 
extra  cement  to  the  batch  of  concrete  to  be  placed  in  the  head  of 
the  pile.  It  is,  of  course,  understood  that  when  a  pile  acts  as  a 
column  that  it  is  to  be  designed  as  a  column. 

The  New  York  City  building  code  as  recommended  by  the 
National  Board  of  Fire  Underwriters,  allows  a  maximum  load 
of  25  tons  per  square  foot  of  cross-section  and  an  additional 
load  of  6000  pounds  per  square  inch  of  steel  reinforcement  in 
the  section.  The  unit-stress  on  the  concrete  is  therefore  nearly 
350  pounds  per  square  inch. 

In  a  given  railroad  pier  foundation  the  piles  were  designed  for 
a  safe  load  of  50  tons.  They  are  octagonal  in  form,  the  least 
diameter  is  12^  inches  and  the  reinforcement  consists  of 
four  | -inch  square  bars.  If  in  this  case  the  compression  on  the 
steel  bars  be  assumed  as  10000  pounds  per  square  inch,  the 
compression  in  the  concrete  is  found  to  be  534  pounds  per 
square  inch. 


136  CONCRETE   PILES  CHAP.  IV 

As  the  design  of  reinforced- concrete  piles  is  so  comparatively 
new,  engineering  practice  in  regard  to  safe  unit-stresses  is  not 
reduced  to  such  narrow  limits  as  in  many  other  divisions  of 
structural  design.  For  a  discussion  of  the  principles  involved 
and  their  application  to  illustrative  examples  the  student  is 
referred  to  standard  text-books  on  mechanics  and  on  reinforced 
concrete. 

The  method  of  computing  the  lateral  resistance  of  a  pile  is 
similar  to  that  for  the  lateral  resistance  of  a  track  spike  as 
deduced  in  JACOBY'S  Structural  Details,  Art.  8.  In  that  case 
the  maximum  unit-compression  on  the  wood  is  located  at 
the  upper  surface  but  for  a  pile  the  bearing  resistance  of  the 
upper  strata  of  the  ground  may  be  less  than  that  of  the  lower 
strata.  Therefore,  while  using  the  same  general  method,  the 
formulas  given  cannot  usually  be  employed  without  some  modi- 
fication. It  may  be  sufficient  for  practical  purposes  in  many 
cases  to  assume  the  surface  of  the  ground  to  be  lowered  more 
or  less  so  as  to  make  the  resultant  moment  of  the  actual  pres- 
sures equivalent  to  that  of  the  theoretic  pressure  used  in 
deducing  the  formula. 

Under  retaining  walls  where  the  piles  receive  a  lateral  thrust 
as  well  as  a  vertical  load  it  is  necessary  to  use  reinforced  piles 
to  resist  the  flexure  thus  produced.  The  distribution  of  bend- 
ing moments  indicates  that  at  least  the  upper  part  of  the  pile 
should  have  a  uniform  section. 

ART.  45.     CAST-IN-PLACE  PILES 

A  cast-in-place  pile  is  a  concrete  pile  which  is  built  in  its 
permanent  place  in  a  hole  prepared  for  the  purpose.  While 
only  some  types  of  the  class  of  pre-molded  piles  are  patented, 
all  types  of  cast-in-place  piles  have  been  patented.  The 
characteristic  features  of  the  latter  class  relate  more  specifically 
to  the  method  of  construction  for  each  type  and  the  appliances 
used  for  that  purpose.  In  making  the  type  known  as  the 
Raymond  pile  (see  Art.  39)  a  tapering  sheet-steel  shell  or  casing 
is  driven  into  the  ground  by  means  of  a  collapsible  steel  core 


FIG.  450. — Two  Sections  of  Reinforced  Sheet-steel  Shell  and  '  Boot'  Section. 
FIG.  456. — Steel  Pile  Driver  of  the  Raymond  Concrete  Pile  Company. 

(Facing  p.    136.) 


ART.  45  CAST-IN-PLACE  PILES  137 

which  acts  as  a  form  to  support  the  shell.  After  the  desired 
penetration  is  reached  the  core  is  collapsed  and  withdrawn,  and 
the  casing  filled  with  concrete.  The  core  when  dressed  with  the 
shell  is  driven  by  means  of  a  pile-driver  with  a  heavy  steam- 
hammer.  On  account  of  the  great  weight  of  the  core  the  pile- 
driver  is  of  heavy  construction,  steel  leads  and  bracing  being 
always  used  for  the  largest  cores.  The  driver  illustrated  in 
Fig.  456,  is  equipped  with  leads  measuring  57  feet  from  the  top 
of  the  turntable  I-beams  to  the  head  block.  The  shell  of  18 
to  20  gage  sheet  steel  is  made  in  various  diameters  and  in  conical 
sections  about  8  feet  long  which  overlap  tightly  (in  telescope 
fashion)  when  in  place,  but  enable  them  to  be  shipped  'knocked 
down/  and  to  be  readily  slipped  over  the  core  in  regular  suc- 
cession. The  very  short  section  closed  at  the  bottom  is  called 
the  'boot/  and  is  made  of  pressed  steel  to  withsand  the  cutting 
effect  of  stone  or  other  obstacles  encountered  in  driving. 

The  object  of  the  casing  is  to  prevent  the  earth  and  water  from 
mixing  with  the  concrete  and  to  act  as  a  mold  that  shall  pre- 
serve its  shape  until  the  concrete  is  set.  Before  placing  the 
concrete,  the  interior  of  the  shell  can  be  inspected,  by  means  of 
an  electric  light,  by  light  reflected  from  a  mirror,  or  by  the  light 
reflected  from  the  surface  of  water  thrown  into  the  casing. 

More  or  less  difficulty  has  been  met  when  the  hydrostatic 
pressure  collapsed  the  thin  shell,  and  sometimes  several  shells 
were  driven  inside  of  one  another.  In  1911  their  construction 
was  improved  by  reinforcing  a  24-gage  shell  with  a  J-inch  wire 
spiral,  as  illustrated  in  Fig.  450,  thus  materially  increasing  its 
strength.  The  concrete  is  either  a  1-2-4  or  a  I~3~5  mixture, 
using  respectively  f-inch  and  if-inch  stone  or  gravel,  and 
mixed  rather  wet. 

The  piles  are  occasionally  reinforced  by  longitudinal  bars 
but  usually  no  such  reinforcement  is  employed,  unless  short 
rods  are  inserted  to  assist  in  bonding  the  tops  of  the  piles  to  the 
concrete  footing.  Lateral  reinforcement  is,  however,  provided 
by  the  spiral  wire  used  to  stiffen  the  casing,  since  the  concrete 
of  the  finished  pile  is  wrapped  by  it.  Since  reinforcement 
is  seldom  used  in  these  piles  it  is  easy  to  place  the  con- 


138  CONCRETE   PILES  CHAP.  IV 

crete  in  the  smooth  shell  so  as  to  obtain  good  concrete  with- 
out voids. 

The  standard  sizes  of  Raymond  piles  have  a  diameter  of  20 
inches  at  the  head  for  lengths  of  20  to  30  feet,  and  18  inches  for 
lengths  of  35  to  40  feet.  The  tip  has  a  diameter  of  6  inches  for 
a  length  of  20  feet,  and  8  inches  for  greater  lengths. 

This  type  of  pile  has  been  very  extensively  employed  in 
America,  especially  for  the  foundations  of  buildings.  The 
special  advantage  claimed  for  it  over  those  of  other  concrete 
piles  are  speed  of  placement,  and  economy  due  to  the  large 
taper  (see  Art.  53  for  discussion  of  taper)  whereby  the  length 
is  materially  reduced.  The  taper  adopted  is  greater  than  that 
for  any  other  type  of  pile.  Additional  advantages  over  those  of 
other  types  of  cast-in-place  piles  are  the  inspection  of  the  form 
in  which  the  concrete  is  deposited,  and  the  testing  of  bearing 
power  for  every  pile  by  the  average  penetration  of  the  steel 
core  under  the  final  blows  of  the  hammer.  On  account  of  using 
a  steel  core  it  is  claimed  to  be  possible  to  drive  through  very 
hard  material  which  cannot  be  penetrated  by  any  other  kind 
of  pile  at  reasonable  cost.  Occasionally  a  steel  core  is  broken 
in  such  material  as  compact  earth  containing  boulders. 

The  Simplex  pile  introduced  in  1903  is  made  by  driving  a  steel 
pipe,  with  a  special  shoe  or  'jaw'  to  close  the  bottom,  in  the  same 
manner  as  a  pile,  and  then  filling  the  hole  with  concrete  as  the 
pipe  is  gradually  withdrawn.  The  pipe  must  be  extra  heavy  and 
at  least  as  long  as  the  pile  to  be  formed,  and  the  pile-driver 
must  have  extra  strength  and  equipment  to  pull  out  the  pipe. 
Sometimes  a  cast-iron  or  concrete  shoe  is  used  with  a  projection 
which  fits  into  the  pipe.  The  shoe  remains  in  place  and 
hence  a  new  one  is  needed  for  each  pile.  Where  the  earth  is 
firm  and  compact  an  'alligator  jaw'  attached  to  the  pipe  by 
cable  hinges  is  used  which  opens  automatically  when  the  pipe  is 
withdrawn  to  permit  the  concrete  to  flow  through  it.  A  ram  is 
generally  employed  to  force  each  batch  of  concrete  into  place 
against  the  surrounding  earth  until  the  hole  is  completely  filled; 
this  increases  the  diameter  of  the  pile  somewhat  beyond  that  of 
the  pipe  driven.  In  some  cases  the  pipe  is  first  filled  with  con- 


ART.  45  CAST  IN   PLACE   PILES  139 

crete  and  then  slowly  withdrawn  at  a  uniform  rate,  without  ram- 
ming the  concrete.  The  concrete  is  made  of  a  fairly  wet  1-2-4 
mixture  using  J-inch  stone  or  gravel,  and  which  by  its  weight  is 
expected  to  resist  the  pressure  of  the  soil. 

It  is  claimed,  since  the  concrete  is  forced  into  the  surface  irregu- 
larities of  the  compressed  earth,  that  its  frictional  resistance  is 
greater  than  for  any  other  kind  of  pile  of  equal  diameter  and 
length.  The  indentations,  however,  become  filled  with  com- 
pressed earth  and  become  a  part  of  the  pile  thus  changing  the 
frictional  or  shearing  surface  to  a  more  regular  form.  The  con- 
crete may  also  adhere  to  some  stone  or  gravel  contained  in  the 
surrounding  material. 

Where  the  earth  penetrated  does  not  have  sufficient  stability 
to  retain  its  form  when  the  pipe  is  withdrawn  this  method  cannot 
be  used  without  modification.  Such  a  condition  has  been  met 
by  dropping  into  the  hole,  after  the  first  batch  of  concrete  was 
placed  an  auxiliary  cylindrical  form  of  sheet  metal  of  slightly 
smaller  diameter  than  the  pipe.  After  this  form  is  filled  with 
concrete  the  pipe  is  withdrawn.  This  leaves  some  voids  outside 
of  the  sheet  metal  form  which  will  only  be  filled  by  adjustment 
of  the  surrounding  earth. 

As  an  illustration  of  the  time  saved  in  construction,  it  is  noted 
that  about  4800  Simplex  piles  from  30  to  45  feet  long  and  aggre- 
gating about  162  ooo  linear  feet  were  driven  through  filled 
material  for  the  Terminal  Warehouse  Building  at  Pittsburgh  in 
76  days  by  7  pile-drivers.  In  another  location  piles  48  feet  long 
were  used.  The  practical  limit  to  the  length  is  the  strength  of 
the  equipment  provided  to  pull  out  the  pipe. 

It  is  impossible  to  inspect  the  integrity  of  the  pile,  and  it  is  a 
question  as  to  what  extent  its  strength  may  be  reduced  by  some 
admixture  of  the  concrete  with  adjacent  earth.  In  stiff,  non- 
water  bearing,  or  clay  soils,  where  the  ground  has  no  tendency 
to  flow,  this  is  claimed  to  be  the  cheapest  system  of  installing 
concrete  piles. 

The  'pedestal  pile'  invented  by  HUNLEY  ABBOTT  may  be 
regarded  as  a  modification  of  the  Simplex  pile  by  the  addition  of 
a  bulb-shaped  base  or  pedestal  at  the  foot.  Its  form  is  intended 


140 


CONCRETE   PILES 


CHAP.  IV 


to  take  a  larger  measure  of  advantage  of  a  lower  stratum  of 
higher  bearing  capacity  than  is  done  by  piles  of  the  ordinary 
form.  By  thus  increasing  its  bearing  area  at  the  foot  it  imi- 
tates the  metallic  disk  and  screw  piles  (Art.  57)  which  doubt- 
less suggested  it. 

The  pedestal  pile  requires  the  same  equipment  as  the  Simplex 
pile  except  the  shoe  or  jaw,  and  in  addition  a  steel  core  which 
fits  inside  of  the  pipe  with  its  enlarged  head  engaging  the  top  of 
the  pipe,  and  its  lower  pointed  end  projecting  several  feet  below 


Ground 


FIG.  45c. — The  Process  of  Forming  Pedestal  Concrete  Piles. 

the  pipe.  As  illustrated  in  Fig.  45^,  the  steel  pipe  and  core  are 
first  driven  into  the  ground  and  a  charge  of  concrete  dumped  into 
the  pipe.  The  core  is  next  used  as  a  rammer  to  enlarge  the  hole 
below  the  pipe  laterally  by  pushing  aside  the  concrete,  repeating 
the  process  until  the  concrete  base  has  the  required  volume. 
Finally,  the  pipe  is  filled  with  concrete  and  then  withdrawn. 

The  pipe  employed  is  usually  16  inches  in  diameter  and  f 
inch  thick,  while  the  core  projects  4  or  5  feet  below  the  pipe. 
The  cylindrical  stem  of  the  pile  is  hence  about  17  inches  in 
diameter  and  the  base  roughly  3  feet  in  diameter,  the  volume  of 
the  base  being  about  16  cuoic  feet.  The  diameter  of  the  base, 
for  a  given  volume  of  concrete  used  in  making  it,  depends  upon 
the  nature  of  the  ground  and  its  homogeneity.  If  for  any  reason 
the  earth  should  resist  unequally  on  opposite  sides  of  the  hole 


ART.  45  CAST-IN-PLACE   PILES  141 

the  resulting  form  of  base  would  make  its  reaction  eccentric. 
The  concrete  is  usually  a  1-2-4  mixture  with  the  broken  stone 
or  gravel  limited  to  a  diameter  of  i|  inches. 

The  pedestal  piles  under  the  retaining  wall  of  the  Oregon- 
Washington  Railroad  and  Navigation  Co.  at  Seattle,  Wash., 
were  reinforced  by  six  f -inch  rods  15  feet  long  in  order  to  provide 
against  bending  moments  due  to  the  horizontal  component  of 
the  earth  pressure. 

Cast-in-place  piles  except  the  Raymond  type  cannot  project 
any  distance  above  the  ground  without  the  use  of  special  forms 
at  increased  cost. 

The  Gow  and  Palmer  pile  is  made  by  driving  a  metal  casing  or 
pipe  into  the  earth,  the  inside  of  which  is  kept  empty  by  a  stream 
of  water  under  pressure  until  it  reaches  the  required  depth. 
The  casing  is  then  withdrawn  a  few  feet  and  a  lozenge-shaped 
cutter  lowered  to  the  bottom  of  the  hole.  By  turning  this  tool 
and  at  the  same  time  opening  it  gradually  the  chamber  is  hol- 
lowed out  and  the  earth  removed  by  the  current  of  water.  The 
casing  and  chamber  are  then  pumped  out,  filled  with  concrete 
and  tamped,  the  casing  being  gradually  withdrawn  as  the  con- 
crete fills  the  hole.  Reinforcing  bars  are  pushed  down  into  the 
concrete  to  reinforce  the  stem  of  the  pile  when  desired.  This 
pile  was  originally  designed  in  1904  to  underpin  a  building,  the 
enlarged  base  being  located  in  the  clay  stratum  which  was  over- 
laid by  filling  and  soft  material  to  a  depth  of  20  feet.  The  casing 
was  in  that  instance  put  down  in  5-foot  lengths. 

In  one  location  where  the  original  surface  of  stiff  clay  had  been 
covered  by  15  feet  of  clay  fill  from  adjoining  excavations  it 
was  deemed  best  to  carry  the  load  to  the  underlying  stratum. 
For  this  purpose  holes  10  inches  in  diameter  were  excavated  by 
means  of  a  post-hole  auger  and  then  filled  with  concrete,  the 
clay  sides  being  stiff  enough  to  retain  the  form  of  the  holes. 
The  piles  were  spaced  3  feet  between  centers,  and  the  cost  of  the 
piles  was  33  cents  per  linear  foot,  60  percent  of  which  represents 
the  cost  of  digging  the  holes.  This  extremely  low  cost  is  due  in 
part  to  the  absence  of  any  charge  for  the  installation  of  plant. 

The  chief  objection  to  all  cast-in-place  piles  has  been  based 


142  CONCRETE   PILES  CHAP.  IV 

upon  the  probability  of  injury  to  the  green  concrete  by  driving 
the  forms  for  adjacent  piles.  There  are  other  disadvantages 
which  pertain  only  to  certain  types.  The  precautions  which 
may  be  adopted  to  obviate  these  difficulties  are  discussed  in  the 
next  article. 

ART.  46.     PRECAUTIONS  AGAINST  INJURY 

Since  pre-molded  piles  cannot  be  driven  until  they  are  suffi- 
ciently seasoned,  they  may  be  placed  in  any  order  in  the  required 
foundation.  This  cannot  safely  be  done  with  cast-in-place 
piles.  When  the  core  or  the  pipe  is  driven  for  a  given  pile,  it 
displaces  and  compresses  the  earth  adjacent  to  the  hole  which  is 
formed,  and  the  elastic  earth  tends  to  relieve  its  stress  by 
crowding  back.  Even  if  the  shell,  which  is  left  in  the  hole,  or 
the  weight  of  the  concrete,  when  no  shell  is  employed,  is  able 
to  resist  this  outside  pressure  until  the  cement  is  set,  it  is  very 
probable  that  the  green  concrete  will  be  injured  by  the  vibra- 
tion and  additional  earth  pressure  due  to  driving  adjacent  piles, 
after  the  setting  of  the  cement  has  progressed  to  a  certain  extent 
and  before  its  completion. 

To  determine  its  effect,  two  tests  were  made  before  beginning 
the  pile  work  in  the  foundations  for  the  north  abutment  of 
the  Pittsburgh  and  Lake  Erie  Railroad  bridge  over  the  Ohio 
River  at  Beaver,  Pa.  The  first  test  consisted  of  a  pile  driven 
with  four  others  around  it,  spaced  as  in  the  proposed  foundation 
work,  the  four  being  driven  while  the  test  pile  was  still  soft. 
The  second  test  differed  from  the  first  only  by  allowing  the  test 
pile  to  set  partially  before  the  four  piles  around  it  were  driven. 
The  working  conditions  on  a  large  foundation  are  such  that  the 
second  test  more  nearly  represents  the  actual  conditions  than 
the  first.  After  both  test  piles  were  allowed  30  days  to  set, 
the  first  test  pile  supported  a  load  of  60  tons  for  72  hours  with  a 
settlement  of  Vr  inch,  which  was  recovered  almost  wholly  after 
the  load  was  removed,  while  in  the  other  case,  the  results,  as 
expected,  were  not  good  enough  for  approval.  To  meet  the 
difficulty  developed  by  the  conditions  of  the  second  test,  and 


ART.  46  PRECAUTIONS   AGAINST   INJURY  143 

which  apply  to  all  kinds  of  concrete  piles  formed  in  place,  thus 
recognizing  the  well-known  limitations  of  concrete,  the  following 
specifications  were  adopted  in  1908,  probably  for  the  first  time 
on  such  work,  and  were  strictly  observed: 

The  setting  of  the  concrete  in  any  pile  must  not,  under  any  considera- 
tion, be  disturbed  by  driving  another  pile  or  piles  within  a  radius  less  than 
9  feet  from  it,  center  to  center,  after  a  minimum  interval  of  three  hours 
or  before  the  expiration  of  seven  days  from  the  time  the  concrete  was  mixed 
with  water  for  that  pile.  The  contractor  may,  however,  at  his  own  op- 
tion drive  pile  forms  within  the  g-foot  radius  to  a  depth  not  more  than  3 
feet  from  the  total  estimated  penetration,  inside  of  the  three-hour  limit; 
and  then  after  the  three-hour  limit  and  before  the  expiration  of  the  seven- 
day  limit,  complete  the  driving  and  filling  of  these  forms. 

The  extent  to  which  such  damage  may  occur  has  been  proved 
by  subsequent  excavation  in  a  number  of  cases,  owing  to  changes 
in  plan  or  to  building  adjacent  structures.  In  one  example, 
failure  was  due  to  the  fluid  alluvial  soil  penetrating  between 
batches  of  concrete,  thus  separating  the  pile  into  sections  about 
5  feet  long.  In  another,  the  cement  failed  to  set  on  account  of 
certain  chemical  constituents  in  the  ground  water,  ascertained 
later  by  analysis.  In  still  other  cases,  piles  had  their  section 
areas  reduced  from  20  to  100  percent;  and  were  bent  out  of  line. 

The  liability  of  the  green  concrete  to  suffer  injury  by  driving 
adjacent  piles  is  increased  when  thin  hard  strata  alternate  with 
soft  ones.  Material,  which  is  lighter  than  concrete,  may 
transmit  pressures  which  displace  concrete  when  it  is  soft,  and 
injure  it  after  the  initial  set.  In  boulders  or  gravel,  a  shearing 
effect  may  be  produced  instead  of  merely  a  direct  pressure. 
Unless  protected  by  a  shell,  there  is  more  or  less  danger  of  some 
of  the  cement  being  washed  out  by  underground  flowing 
water,  or  on  the  other  hand,  that  the  cement  may  be  deprived 
of  some  of  the  water  which  it  needs  to  set  completely,  by  the 
absorbent  earth. 

It  should  be  added  that  the  construction  of  cast-in-place  piles 
requires  more  careful  supervision  to  secure  good  results,  on 
account  of  the  manner  in  which  the  concrete  is  deposited,  and 
the  surrounding  conditions  which  preclude  inspection  of  the 


144  CONCRETE  PILES  CHAP.  IV 

pile  after  the  concrete  is  all  in  place.  When  it  is  deemed  neces- 
sary to  put  reinforcement  in  a  cast-in-place  pile  throughout  its 
length,  it  should  be  fabricated  as  a  unit  and  properly  put  in 
position.  It  is  impracticable  to  place  bars  separately,  so  that 
they  shall  occupy  specified  positions  in  the  finished  pile. 

ART.  47.     COMPOSITE  TYPES  AND  COMBINATION  PILES 

Hollow  pre-molded  piles,  which  were  filled  with  lean  concrete 
after  they  were  placed  in  their  final  positions  were  driven  in  191 1, 
for  the  foundations  of  the  ocean  pier  at  Long  Branch,  N.  J. 
The  piles  are  of  the  Hennebique  type  and  range  in  length  from 
45  to  68  feet,  with  an  average  penetration  of  22  feet.  Near  the 
shore,  some  1 8-inch  square  piles  were  used  but  the  rest  are  hol- 
low square  piles  24  inches  square  on  the  outside  and  13  inches 
on  the  inside,  in  order  to  reduce  their  weight  for  handling. 
The  reinforcement  consists  of  ij-inch  round  rods  tied  together 
at  intervals  with  J-inch  wire  collars,  while  the  longer  piles  have 
additional  reinforcement  in  the  middle  to  provide  against  break- 
age by  handling.  They  were  handled  by  a  special  form  of  sling 
or  bridle,  to  reduce  the  stresses  due  to  bending. 

The  '  peerless'  concrete  pile  has  a  sectional  reinforced  con- 
crete shell,  which  is  driven  down  together  with  a  steel  driving 
pipe,  both  of  which  bear  on  a  pointed  cast-iron  shoe,  which  is 
left  in  the  ground.  After  the  steel  pipe  is  withdrawn,  the  shell 
is  inspected,  and  filled  with  concrete  by  a  special  tremie  de- 
signed for  the  purpose.  The  use  of  the  steel  pipe  protects  the 
concrete  shell  from  severe  stresses  due  to  driving. 

Reinforced-concrete  piles,  with  the  unprecedented  diameter  of 
25  inches,  were  placed  under  the  Music  Hall  at  the  reconstructed 
pier  in  Atlantic  City  in  1906.  Since  the  largest  of  these  piles 
were  nearly  50  feet  long,  it  was  deemed  impracticable  to  mold 
them  complete  before  sinking  them  in  place.  Accordingly,  the 
lower  portion,  12  feet  long,  which  included  an  enlarged  foot, 
3^  feet  in  diameter  and  2  feet  high,  was  molded  in  a  wooden 
form  with  the  jet  pipe  and  steel  reinforcement  in  place.  When 
the  concrete  was  hardened,  a  T\-inch  galvanized  steel  shell 


ART.  47         COMPOSITE   TYPES   AND   COMBINATION   PILES  145 

was  slipped  a  little  distance  over  its  top,  and  the  joint  made 
water-tight  by  calking  with  oakum.  The  steel  shell  was  made 
water-tight  by  close  riveting  and  calking,  and  was  long  enough 
to  reach  above  the  water  when  sunk.  After  the  reinforcement 
of  the  upper  part  of  the  pile  was  hooked  on-  and  the  jet  pipe 
extended,  the  pre-molded  pile  and  casing  were  swung  into  place 
and  sunk  about  16  feet  in  the  sand  by  the  water-jet.  The  steel 
form  was  then  filled  with  concrete. 

Where  the  conditions  are  such  that  the  water-jet  cannot  be 
used  to  sink  them  and  there  is  danger  of  damage  to  pre-molded 
piles  by  driving,  the  following  method  may  be  adopted:  A 
steel  shell  and  cast-iron  shoe  are  driven  to  the  proper  penetra- 
tion by  the  method  used  for  Simplex  piles;  some  concrete  is 
then  placed  in  the  shell  and  a  molded  reinforced-concrete  pile  is 
inserted  and  imbedded  firmly  in  the  concrete  in  the  bottom  of 
the  hole,  after  which,  the  intervening  space  is  filled  with  a  strong 
grout  and  the  shell  is  withdrawn.  The  quantity  of  grout  used 
is  to  provide  some  excess  over  that  required  to  fill  the  space 
between  the  molded  pile  and  the  sides  of  the  hole  after  the  shell 
is  withdrawn. 

This  method  was  specified  for  the  pile  foundations  of  a  rein- 
forced-concrete  structure  of  the  Pittsburgh  and  Lake  Erie 
Railroad  at  Youngstown/  Ohio.  The  molded  piles  were  octag- 
onal in  form,  \2\  inches  thick,  of  uniform  cross-section  through- 
out and  the  lengths  were  determined  by  driving  test  piles.  The 
molded  piles  were  varied  in  length  by  steps  not  exceeding  5 
feet  and  generally  smaller;  and  the  top  of  the  molded  pile  was 
brought  to  the  proper  elevation  by  adjusting  the  quantity  of 
concrete  filling,  which  ranged  in  depth  from  2  to  5  feet  after 
the  shell  was  withdrawn.  The  reinforcing  rods  extended  2  feet 
below  the  bottom  of  the  molded  pile. 

It  was  specified  that  the  Simplex  forms  and  shoes  were  to  be 
driven  to  a  penetration  of  \  inch  per  blow  from  a  3ooo-pound 
hammer,  falling  15  feet.  No  inserted  pile  was  to  be  exposed  to 
stresses  due  to  driving  adjacent  piles,  until  it  had  been  in  place 
15  days.  The  piles  were  designed  to  carry  50  tons  per  pile 
safely,  and  those  selected  for  testing  were  to  settle  not  more  than 


146  CONCRETE   PILES  CHAP.  IV 

a  half-inch  under  a  load  of  60  tons.  It  was  estimated  that  the 
use  of  molded  piles  thus  inserted,  at  an  increased  cost  per  pile, 
would  reduce  the  total  cost  of  the  foundation  by  diminishing  the 
sizes  of  the  pier  footings,  under  the  assumption  that  their  safe 
bearing  power  is  25  percent  greater  than  that  of  cast-in-place 
piles. 

On  the  Pacific  Coast,  combination  piles  have  been  made  for 
wharf  construction  by  driving  a  wooden  pile  from  50  to  60  feet 
long  with  its  head  projecting  10  feet  above  the  mud  line,  which 
is  20  or  30  feet  below  the  top  of  the  wharf.  A  hollow  reinforced- 
concrete  pile  2  to  3  inches  thick  and  24  inches  in  diameter  is  then 


FIG.  470. — Ripley  Combination  Pile. 

driven  over  the  wooden  pile  to  a  good  bearing  in  the  mud. 
After  removing  the  mud  and  water  inside,  the  hollow  pile  is  filled 
with  concrete.  Such  combination  piles  can  also  be  used  in 
foundations  on  land,  and  are  considerably  cheaper  than  very 
long  concrete  piles. 

Similar  combination  piles  were  used  in  the  Delaware  Lacka- 
wanna  and  Western  Railroad  Terminal  at  Hoboken,  N.  J., 
but  in  this  case  the  form  for  the  concrete  top  was  attached  to 
the  pile  and  carried  down  with  it  into  position  so  as  to  avoid  the 
necessity  of  pumping  out  the  form.  The  forms  were  filled  after 
the  follower  was  withdrawn. 

Occasionally  the  durability  of  concrete  piles  is  combined  with 
the  lesser  weight  and  cost  of  timber  piles,  in  a  single  building 
foundation  by  placing  concrete  piles  on  top  of  timber  piles,  which 


ART.  48  DRIVERS,   HAMMERS,   AND   CAPS  147 

are  driven  below  ground  water  level  with  the  aid  of  a  follower. 
In  case  the  concrete  pile  is  built  in  place,  a  waterproof  tube  or 
container  is  put  on  top  of  the  timber  pile,  filled  with  concrete, 
and  after  the  concrete  is  hardened  sufficiently,  the  upper  end 
of  the  container  is  cut  away  at  the  lower  surface  of  the  concrete 
cap  or  footing. 

The  Ripley  combination  pile,  shown  in  Fig.  470  is  composed 
of  a  timber  pile  encased  in  concrete.  The  reinforcement  con- 
sists of  wire  mesh  wound  spirally  with  the  concrete  around  the 
pile  to  which  it  is  attached  by  staples,  the  final  lap  being  tied 
with  wire.  Before  concreting,  spikes  are  driven  into  the  timber 
at  intervals  on  its  surface.  The  concrete  is  a  1-2-3  mixture  of 
cement,  sand,  and  broken  stone. 

ART.  48.     DRIVERS,  HAMMERS,  AND  CAPS 

To  drive  pre-molded  piles  the  pile-driver  and  its  equipment 
have  to  be  strong  on  account  of  the  greater  weight  to  be  handled, 
and  the  heavier  hammers  used.  Piles  weighing  from  2  to  4 
torts  are  quite  common  and  those  of  6  to  8  tons  are  employed 
on  heavy  construction.  On  this  account  the  steel  pile-driver  is 
growing  in  favor.  It  is  found  to  be  stiffer,  more  durable,  and 
lighter  for  the  same  strength  than  those  built  of  wood.  The 
necessity  for  dragging  the  piles  from  the  casting  platform  or 
from  the  unloading  platform  to  the  driver  develops  stresses 
in  the  tower  for  which  special  provision  must  be  made  in 
the  design. 

Concrete  piles  should  be  driven  wherever  possible  with  the 
aid  of  the  water-jet  so  that  the  duty  of  the  hammer  becomes 
secondary.  However,  in  some  kinds  of  earth  it  is  necessary  for 
the  hammer  to  do  very  effective  work  either  with  or  without 
the  aid  of  the  water-jet.  Under  such  conditions  it  is  uneconom- 
ical to  use  a  light  hammer  which  may  answer  very  well  for  a 
timber  pile  but  which  itself  is  considerably  lighter  than  a  con- 
crete pile.  Otherwise  the  temptation  is  constantly  present  to 
use  too  high  a  fall  and  thus  expend  too  large  a  part  of  the  energy 
in  useless  or  destructive  work. 


148  CONCRETE   PILES  CHAP.  IV 

In  driving  concrete  piles  into  hard  clay  for  the  foundations 
of  the  Kentucky  and  Indiana  Bridge  to  which  reference  was 
made  in  Art.  43,  a  steam-hammer  was  at  first  used  in  which  the 
striking  parts  weighed  3000  pounds.  Upon  substituting 
another  one  with  a  6ooo-pound  striking  weight  the  results 
were  far  more  satisfactory. 

Although  drop-hammers  weighing  less  than  4000  or  5000 
pounds  have  been  employed  to  drive  concrete  piles  successfully 
the  time  required  was  unnecessarily  large  to  secure  the  required 
total  penetration.  Very  satisfactory  results  have  been  secured 
on  some  building  foundations  in  Pittsburgh  by  using  hammers 
weighing  from  7000  to  12000  pounds  each.  Such  hammers  are 
handled  by  three-part  crucible-steel  lines  rove  at  the  lower  end 
over  sheaves  set  in  the  hammer  casting.  The  fall  of  the  largest 
hammer  is  limited  to  about  8  feet,  but  is  usually  less,  and  it  has 
been  used  to  drive  concrete  piles  weighing  about  3000  pounds 
to  an  average  depth  of  30  feet  below  the  surface  with  a  penetra- 
tion in  the  gravel  of  i  inch  for  the  last  ten  blows  of  the  hammer. 
Three  machines  operated  by  a  total  crew  of  25  men,  have  aver- 
aged 15  piles  per  day  for  each  machine,  with  a  maximum  of  25 
piles,  while  driving  through  mud  and  clay  which  overlay  a  deep 
gravel  stratum. 

The  heaviest  steam-hammer  built  prior  to  1913  was  an  Arnott 
make  with  a  total  weight  of  28  ooo  pounds  and  with  striking 
parts  weighing  4000  pounds.  Its  length  of  stroke  is  36  inches. 
It  was  especially  designed  to  drive  concrete  piles  24  inches  square 
and  47  to  77  feet  long  for  the  monolithic  concrete  piers,  docks 
and  breakwaters  of  the  Canadian  Government  at  Halifax,  N.  S. 
A  single-acting  hammer  has  been  built  with  moving  parts 
weighing  7500  pounds,  and  a  total  weight  of  16000  pounds. 
Those  who  have  had  experience  with  both  steam-  and  drop- 
hammers  in  driving  concrete  piles  state  that  the  steam-hammer 
drives  them  in  less  time  and  with  less  injury  to  the  pile.  Excel- 
lent results  have,  however,  been  obtained  with  the  drop- 
hammer,  the  heavier  hammers  being  the  more  efficient. 

The  successful  driving  of  pre-molded  piles  without  injury, 
when  it  is  necessary  to  use  the  hammer  actively,  is  due  mainly 


ART.  48 


DRIVERS,    HAMMERS,    AND    CAPS 


149 


to  the  various  driving  caps  which  have  been  devised  as  the 
result  of  experience.  Fig.  480  shows  the  form  used  for  the 
foundation  pile  of  the  Municipal  bridge  approach  at  -St.  Louis. 
The  construction  is  fully  explained  on  the  diagram.  It  was 
found  that  as  long  as  the  blow  could  be  uniformly  distributed 
on  the  pile  head  but  little  injury  was  produced,  but  when  the 


Casi- Steel 
Striking  Piece 


Drift  Hole  for      \ 
removing  the 
Oak  driving  BlockX 
when  worn  out 


Oak  Driving  Block 

-  -Steel  Casting 

irLuqs  to  fit 
Leads  of  Driver 

-Layers  of  Old 
Rubber  Belting 


-Band  of  l"Steel  PI. 
bolted  around  Pile 
to  prevent  spa  I  ling 


-Reinforced 
Concrete  Pile 


FIG.  48a. — Cap  for  Driving  Concrete  Piles. 

pressure  was  too  large  on  the  edges  the  pile  head  spalled  and 
exposed  the  reinforcing  bars.  Hence  in  some  cases  the  head  had 
to  be  cut  off  in  order  to  continue  driving. 

Fig.  486  gives  the  details  of  the  shells  of  two  driving  caps 
which  have  been  used  on  the  Chicago,  Burlington  and  Quincy 
Railroad.  The  steel  cap  which  was  first  used  consists  of  a 
built-up  shell  of  f -inch  plate,  with  steel  channel  guides  riveted 
to  the  sides.  The  extension  guides  are  to  keep  the  cap  in  the 
leads  when  driving  below  the  track,  thus  avoiding  delay  in 
reentering  it.  Near  the  lower  end  of  the  shell  is  fitted  a  3 -inch 
oak  block  and  above  that  a  6-inch  layer  of  rope  ends,  old  rubber 
hose  or  belting.  Resting  on  top  of  this  cushion  is  a  short  piece 
of  wooden  pile  which  extends  above  the  guides  and  receives  the 
blows  of  the  hammer.  For  use  with  the  cast-iron  cap,  the 
cushion  consists  of  two  layers  of  old  rope  or  a  bag  of  sawdust. 


CONCRETE   PILES 


CHAP.  IV 


After  the  pile  is  placed  in  position  the  cushion  is  laid  on  top  of 
its  head  and  the  cap  lowered  over  it.  The  top  of  the  cap 
contains  a  short  driving  block.  As  shown  in  the  plan  this  cap 
is  designed  to  fit  either  a  round  or  a  square  pile.  Its  jaws  are 
chamfered  at  the  top  to  facilitate  reentering  the  leads  when  it 


3 


Section  through  Extension 
Guides 

Sr 


Section  E-E          Detail  of  Hoist  Strap 
Steel  Driving  Cap 

FIG.  486. — Steel  and  Cast- Iron  Shells  of  Pile  Caps. 

is  driven  below  them.  The  cast-iron  cap  was  found  to  be  more 
satisfactory  in  service  than  the  steel  cap  in  which  the  rivets 
holding  the  angles  broke  repeatedly.  The  cap  used  in  pile 
driving  at  the  Kentucky  and  Indiana  bridge  at  Louisville  was 
square  in  cross-section,  and  composed  of  two  bent  steel  plates 
bolted  together  through  the  projecting  flanges  at  the  sides.  On 
the  other  two  sides  channels  to  engage  the  leads  were  riveted 


ART.  48  DRIVERS,   HAMMERS,    AND    CAPS  151 

by  means  of  two  pairs  of  intermediate  horizontal  Z-bars.  After 
a  number  of  experiments  with  cushions  the  best  results  were 
obtained  by  placing  three  cement  bags  filled  with  coarse  sawdust 
directly  on  the  head  of  the  pile  which  projected  several  inches 
up  into  the  steel  cap.  A  square  block  of  beechwood  2  feet  long 
was  placed  on  top  to  receive  the  blows  of  the  hammer.  This 
species  of  wood  proved  better  than  any  other.  In  some  cases 
where  fine  sawdust  was  used  the  pile  heads  shattered  under 
very  hard  driving. 

At  the  Cleveland  docks  of  the  Pennsylvania  Lines  (see  Art. 
41)  a  cast-iron  cap  was  used  with  an  oak  filler  block  on  top  and 
a  few  coils  of  rope  underneath.  At  Cambridge  (see  Art.  49)  the 
steel-plate  cap  was  16  inches  square  on  the  inside  and  inclosed 
an  oak  block  18  inches  high,  to  the  bottom  of  which  six  thick- 
nesses of  rope  and  four  layers  of  rubber  belting  were  nailed. 
The  cap  was  held  in  the  leads  by  two  pairs  of  vertical  oak  pieces 
bolted  through  the  incased  driving  block.  At  Brunswick 
(see  Art.  41)  a  cast-steel  cap  was  used  with  rope  and  rubber 
below  and  a  wooden  driving  block  above.  The  cap  was  made  to 
fit  over  the  tenon  cast  on  the  head  and  performed  the  important 
additional  function  of  preventing  the  pile  from  turning  while 
it  was  being  driven.  At  the  Chicago  and  Northwestern  Railway 
bridge  at  Racine,  Wis.,  the  cast-steel  cap  was  3  feet  high  and 
had  a  solid  horizontal  diaphragm  in  the  middle.  The  underside 
fitted  the  pile  and  rested  directly  on  its  head.  On  top  of  the 
diaphragm  was  placed  a  rubber  cushion  and  driving  block. 

In  another  case  the  cushion  in  the  casting  is  composed  of 
coarse  sawdust  or  planing-mill  shavings,  above  which  rested 
a  hard  gum  driving  block  hooped  with  a  steel  ring.  The  sawdust 
or  shavings  are  quickly  compressed  to  adhere  to  the  casting  and 
only  need  occasional  renewal.  The  driving  block  proved  to  be 
very  durable.  Sometimes  rubber-lined  canvas  hose  is  combined 
with  rope  to  form  a  cushion.  In  still  another  example,  a  mat 
of  six  layers  of  rope  was  placed  on  the  pile  head  below  the  dia- 
phragm of  the  cast-iron  cap  while  sawdust  and  a  hooped  driving 
block  were  placed  above  it.  Australian  pine  has  also  been 
employed  for  driving  blocks. 


152  CONCRETE  PILES  CHAP.  IV 

ART.  49.    DRIVING  CONCRETE  PILES 

Some  of  the  difficulties  encountered  in  keeping  the  pipe  from 
clogging  when  the  jet  pipe  is  cast  in  the  pile,  are  due  to  improper 
construction  of  the  nozzle.  In  ground  containing  a  large  pro- 
portion of  sand  the  sinking  can  be  done  mainly  by  the  use  of  the 
jet,  the  hammer  serving  merely  as  a  weight  or  to  give  occasional 
light  blows.  Where  clay  is  the  predominant  constituent  of  the 
ground  the  nozzle  clogs  frequently  when  the  hammer  is  actively 
employed.  This  difficulty  can  be  overcome  most  readily  by 
extending  the  diameter  of  the  end  of  the  nozzle  back  for  12 
inches  or  more,  thus  substituting  a  short-pipe  tip  for  a  conical 
tip.  For  concrete  piles  it  is  generally  preferable,  however,  to 
use  two  jets  on  the  outside  of  the  pile.  The  equipment, 
methods,  and  precautions  for  the  use  of  the  water-jet  described 
in  Art.  17  apply  likewise  topre-molded  concrete  piles.  The  use 
of  the  water-jet  with  adequate  equipment  in  sinking  concrete 
piles  whenever  sub-surface  conditions  permit,  is  to  be  urged  not 
merely  on  account  of  avoiding  any  possible  injury  to  the  pile  by 
driving  with  a  hammer  but  to  save  time  and  energy. 

At  Brunswick,  Ga.,  after  failing  to  make  satisfactory  progress 
by  means  of  the  jet  and  hammer  a  new  scheme  was  adopted,  in 
which  the  pile  itself  was  used  as  a  hammer.  A  wire  bridle  was 
fastened  near  the  top  of  the  pile  by  which  to  lift  it,  but  the  cap 
and  hammer  were  allowed  to  remain  on  top  to  give  additional 
weight.  The  pile  was  raised  from  1 8  to  24  inches  and  dropped, 
and  while  this  process  was  continued  the  jet  was  constantly 
operated,  until  the  driving  was  nearly  completed.  By  this 
means  the  number  of  piles  driven  per  day  was  increased  to  six- 
fold. The  water  was  then  shut  off  and  the  last  few  inches  driven 
by  the  hammer  alone.  This  distance  was  increased  to  8  or  10 
inches  in  good  clear  sand,  as  the  jet  excavated  deeper  below  the 
foot  than  in  the  other  material.  The  ground  penetrated  varied 
from  clear  sand  to  hard  clay.  It  was  also  necessary  to  penetrate 
a  2-foot  stratum  of  soft  rock  composed  of  shells,  sand  and  lime 
which  was  harder  than  any  coral.  About  50  percent  of  the  6000 
piles  had  to  be  driven  through  that  material.  Upon  taking  up 


ART.  49  DRIVING  CONCRETE   PILES  153 

some  piles  driven  through  it  the  edges  at  the  foot  were  found  to 
be  but  slightly  rounded  off.  The  jet  pipe  was  not  reduced  in 
diameter  at  the  end,  and  the  pipe  did  not  clog  from  driving 
more  than  once  or  twice.  Their  dimensions  are  given  in  the 
ninth  paragraph  of  Art.  41. 

At  the  Charleston,  S.  C.,  pier  the  bottom  consisted  of  marl 
containing  a  yellow  clay  and  about  15  percent  of  sand,  making 
it  extremely  hard  and  sticky.  When  exposed  to  the  air  for  a 
few  hours  it  required  a  hammer  to  break  it.  Some  of  the  piles 
(see  Art.  41)  had  to  be  driven  through  38  feet  of  the  marl,  and 
this  was  accomplished  entirely  by  the  churning  process  until 
within  2  or  3  inches  of  the  full  penetration  when  they  were  driven 
to  grade  by  a  45oo-pound  hammer. 

In  driving  800  3o-foot  concrete  piles  for  the  Sixth  Street 
Viaduct  in  Kansas  City,  Mo.,  a  hole  was  jetted  down  the  full 
length  of  the  pile  in  the  proper  position.  The  pile  was  then 
inserted  in  the  hole  and  churned  up  and  down  with  the  hammer 
resting  on  top,  while  the  jet  was  used  alongside  of  the  pile. 
Experience  showed  that  two  jets  would  have  been  better  to 
secure  sinking  accurately  in  position.  When  the  hole  was  not 
first  jetted  down  the  piles  had  a  tendency  to  crowd  toward  those 
previously  driven  since  the  ground  on  that  side  was  still  soft. 

At  Cambridge,  Mass.,  where  a  47oo-pound  drop-hammer  and 
water-jet  were  used  in  driving  piles  for  a  building  foundation,  it 
was  found  best  to  begin  driving  by  churning  and  the  water-jet, 
and  after  continuing  this  method  as  long  as  possible  the  chain 
which  connected  the  pile  to  the  hammer  during  the  churn- 
ing operation  was  disconnected  and  the  hammer  started  with  a 
drop  of  about  2\  to  4  feet,  and  increasing  the  fall  as  the  driving 
became  harder.  Sometimes  the  churning  process  can  be 
employed  advantageously  to  start  a  pile  in  cases  where  the 
leads  are  not  long  enough,  or  a  short  wooden  pilot  pile  may 
be  driven  first  and  withdrawn,  and  the  pile  then  churned  up 
and  down  in  the  hole  after  directing  a  stream  of  water  into  it 
with  the  hose. 

In  loam  and  ordinary  clay  it  was  the  practice  on  the  Burling- 
ton Railroad,  as  reported  in  191 1,  to  put  down  two  or  three  holes 


154  CONCRETE   PILES  CHAP.  IV 

with  the  jet  as  close  together  as  possible.  The  pile  was  then 
set  in  the  leads  and  driven  without  further  use  of  the  jet.  It 
was  found  that  this  method  saves  time  besides  reducing 
injury  to  the  pile.  In  many  cases  a  penetration  was  thus 
secured  which  could  not  have  been  reached  by  driving  with  the 
hammer  alone. 

In  order  to  save  a  considerable  length  of  pipe  an  arrangement 
is  sometimes  adopted  of  casting  a  jet  pipe  only  in  the  lower  por- 
tion of  the  pile,  its  upper  end  having  a  reversed  curve  and 
terminating  outside  of  the  pipe.  The  outside  pipe  can  then  be 
connected  to  this  and  afterward  removed.  This  connection 
may  be  located  just  above  the  ground  level  in  a  pile  extending 
above  the  water  surface. 

It  is  remarkable  how  well  pre-molded  piles  usually  stand  the 
pounding  of  the  hammer  where  the  jet  cannot  be  used  success- 
fully. In  one  instance  where  piles  were  driven  into  hard  clay 
for  a  bridge  pier,  after  several  piles  were  driven  the  clay  became 
so  compact  that  it  required  5000  blows  of  the  steam-hammer  to 
drive  some  of  them  20  feet.  In  the  few  piles  which  were  broken 
the  crushing  extended  only  18  inches  below  the  top  of  the  head. 
At  the  approach  to  the  Municipal  bridge  where  the  driving 
was  very  hard  only  eight  out  of  767  piles  were  broken,  due  to  the 
cold  weather  retarding  the  setting  of  the  concrete.  Apart  from 
this  the  injury  to  other  piles  was  confined  to  some  spalling  at  the 
heads,  and  that  occurred  mainly  in  piles  made  in  the  winter. 
In  some  cases,  piles  stood  40  to  80  blows  per  inch  of  penetration, 
but  most  of  the  heads  were  uninjured  after  sustaining  more  than 
2000  blows  of  a  steam-hammer. 

Reinforced-concrete  piles  made  in  cold  weather  and  im- 
perfectly set  due  to  the  cold,  can  be  driven  practically  without 
fracture  at  low  temperatures,  or  about  10  to  15  degrees  Fahren- 
heit. When,  however,  the  temperature  rises  above  the  freezing 
point,  such  piles  will  go  to  pieces  under  the  hammer.  But  after 
the  piles  are  thoroughly  cured  they  can  be  driven  without 
danger  of  fracture.  In  other  words,  in  respect  to  driving,  the 
effect  of  freezing  is  practically  the  same  as  that  of  thorough  set- 
ting of  the  concrete. 


ART.  49  DRIVING  CONCRETE   PILES  155 

In  driving  675  concrete  piles,  molded  vertically  in  steel  forms, 
to  a  penetration  of  20  to  30  feet  for  bridge  piers  in  Cleveland, 
no  failures  occurred  and  no  pile  heads  were  battered.  A  five- 
ton  steam-hammer  was  used.  Thoroughly  well-seasoned  con- 
crete piles  will  stand  without  appreciable  injury  several  hundred 
blows  with  a  3ooo-pound  drop-hammer,  the  drop  increasing 
from  10  to  30  feet  as  driving  progresses,  but  comparatively 
green  piles  must  be  handled  very  carefully  and  the  drop  limited 
to  6  or  8  feet.  Such  work  is  slow  and  expensive,  and  it  is 
better  to  season  piles  thoroughly. 

In  driving  3-ton  piles  under  bridge  abutments  by  the  Sanitary 
District  of  Chicago,  the  time  ranged  from  9  to  27  minutes  per 
pile  for  the  driving,  with  21  minutes  or  more  to  get  the  next 
pile  ready.  The  average  number  of  blows  was  600,  and  the 
maximum  1782.  One  of  the  piles  which  required  over  1600 
blows  was  cut  off  i|  feet,  and  no  lines  of  weakness  due  to  driving 
could  be  discovered.  Of  300  octagonal  piles  driven  by  the 
Long  Island  Railroad  on  its  Jamaica  improvements  not  a 
single  one  was  broken  either  in  handling  or  in  driving. 

In  1907  a  pre-molded  pile  30  feet  long  in  which  the  reinforce- 
ment was  electrically  welded  into  a  unit  form,  was  selected  at 
random  from  a  thousand  that  had  been  driven  for  a  dock  pier. 
A  careful  examination  of  the  pile  after  it  was  pulled  up  failed  to 
reveal  any  defects.  The  same  pile  was  thereupon  driven  and 
withdrawn  twice  in  different  locations  through  20  feet  of  silt, 
sand  and  gravel  into  soft  rock,  without  any  sign  of  deterioration. 
Finally  it  was  driven  again  for  permanent  use  in  the  pier. 

At  Cambridge  in  1908  a  reinforced-concrete  pile  struck  a 
boulder  at  a  depth  of  about  18  feet  and  could  be  driven  no 
further.  The  47oo-pound  hammer  with  drops  of  18  to  30 
inches  had  given  it  735  blows,  the  water- jet  being  used  also.  As 
the  head  was  badly  crushed  the  driving  was  stopped;  the  pro- 
jecting part  was  cut  off,  its  ends  squared,  and  sent  to  the  Water- 
town  Arsenal  for  test.  Its  length  was  g\  feet,  its  smaller  section 
area  128.59  square  inches,  and  it  developed  a  compressive 
strength  of  3865  pounds  per  square  inch.  Since  this  value 
exceeds  the  usual  strength  of  reinforced  concrete  columns,  the 


156  CONCRETE   PILES  CHAP.  IV 

pile  evidently  suffered  no  injury  due  to  hard  driving  except 
at  the  head  which  was  cut  off. 

Another  method  has  been  used  in  hard  clay  which  resisted 
penetration  by  the  use  of  the  steam-hammer  except  at  too  great 
a  cost  in  time.  The  piles  were  14  and  9  inches  square  at  the 
butt  and  tip  respectively,  22  feet  long  and  driven  to  rock. 
Holes  12  inches  in  diameter  were  bored  with  a  post-hole  auger 
from  1 6  to  19  feet  deep  in  which  to  place  the  pile  and  start 
driving.  The  weight  of  the  hammer  would  push  the  pile  down 
8  to -i  i  feet.  In  driving  the  piles  great  care  was  necessary  to 
center  the  leads  directly  over  the  piles  so  as  not  to  cause  bending 
in  the  pile.  Only  one  out  of  125  piles  was  shattered  enough  to 
condemn  it,  and  only  three  required  new  heads  to  be  cast. 
After  gaining  some  experience  90  percent  could  be  driven  with- 
out a  crack,  and  in  the  balance  the  cracks  were  confined  to  the 
topmost  12  inches.  It  was  found  necessary  to  stop  driving  at 
intervals  to  permit  the  compressed  air  and  water  in  the  auger 
hole  to  escape  through  the  gravel  next  to  the  rock. 

In  Art.  47  reference  was  made  to  a  method  which  avoids  driv- 
ing the  concrete  pile  itself,  by  first  driving  a  very  heavy  steel 
tube  fitted  with  a  point  or  shoe.  After  it  has  penetrated  to  a 
good  bearing,  a  few  cubic  feet  of  concrete  are  deposited  in  the 
bottom  of  the  form.  A  pre-molded  pile,  slightly  smaller  in 
diameter  than  the  tube,  is  then  lowered  to  place  and  forced 
into  the  plastic  concrete.  After  withdrawing  the  tube  the 
remaining  space  is  filled  with  grout.  By  this  method  a  pile 
may  be  forced  some  distance  into  stiff  clay  or  hard-pan  which 
is  overlaid  by  soft  material  that  would  not  otherwise  hold  the 
pile  in  place  1  aterally. 

Concrete  piles  cannot  be  driven  as  rapidly  as  timber  piles 
on  account  of  the  care  necessary  in  handling  the  greater  weights, 
and  the  extra  work  in  getting  ready  to  drive,  as  well  as  the 
necessary  delays  incidental  to  driving.  In  one  case  where 
three  crews  were  working  on  the  same  foundation,  one  drove 
41  piles  aggregating  1207  linear  feet  in  872  hours,  another  39 
piles  or  1130  linear  feet  in  9  hours,  and  the  third  45  piles  or  1064 
linear  feet  in  10  hours.  In  another  case  42  piles  were  driven  in 


ART.  50  ANALYSIS   OF   TIME  AND   COST  157 

10  hours.  No  soil  has  been  encountered  in  which  wooden 
piles  can  be  driven  in  which  it  has  not  been  possible  to  drive 
concrete  piles,  and  in  many  cases  with  far  less  danger  of  over- 
driving. At  Greenville,  N.  J.,  a  Chenoweth  pile  13  inches  in 
diameter  and  50  feet  long  was  driven  into  the  ground  and  pene- 
trated 8  feet  into  a  substratum  of  gravel,  and  subsequently  with- 
drawn. A  wooden  pile  could  be  driven  only  2  feet  into  it. 

Occasionally  it  is  found  to  be  impossible  to  drive  a  concrete 
pile  to  the  proposed  depth,  and  it  becomes  necessary  to  cut  off 
its  head  to  a  given  grade  to  connect  with  a  concrete  footing. 
A  track  chisel  and  heavy  hammer  may  be  used  for  the  concrete 
and  a  hack  saw  for  the  reinforcing  bars.  A  plumber's  pipe 
cutter  has  also  been  used  for  round  reinforcing  rods.  Since 
the  concrete  is  usually  not  more  than  a  month  old  when  driven 
the  task  of  cutting  it  is  not  as  difficult  as  for  concrete  which  is 
thoroughly  seasoned. 

ART.  50.    ANALYSIS  OF  TIME  AND  COST 

In  order  to  obtain  data  for  estimates  of  cost  for  pile  driving 
a  series  of  observations  was  made  in  1908  by  SANFORD  E. 
THOMPSON  and  BENJAMIN  Fox,  of  the  time  required  for  each 
elementary  operation  into  which  the  process  of  pile  driving  was 
analyzed.  The  results  in  detail  together  with  the  conclusions 
and  some  recommendations  intended  to  facilitate  pile  driving 
operations  by  better  system  and  less  waste  of  time  are  published 
in  the  Journal  of  the  Association  of  Engineering  Societies,  vol. 
42,  page  i,  January,  1909. 

The  ground  at  the  site,  as  was  shown  by  explorations,  con- 
sisted of  6  to  8  feet  of  fill;  and  then  to  a  depth  of  29^  to  31^ 
feet  from  the  surface,  fine  sand  and  mud,  but  which  was  prac- 
tically considered  all  sand;  underlaid  by  a  clay  hard-pan  which 
was  tested  to  a  depth  of  13  feet.  The  piles  were  14  and  9 
inches  square  at  the  butt  and  tip,  each  one  being  reinforced  by 
four  | -inch  corrugated  bars  with  loops  of  J-inch  bars  spaced 
about  12  inches  apart  but  reduced  to  4  inches  near  the  head. 
Extra  longitudinal  reinforcement  of  f -  or  |-inch  bars  2  or  3  feet 


158  CONCRETE  PILES  CHAP.  IV 

long  was  also  put  in  the  head.  A  galvanized  pipe  was  cast  in 
the  center  of  each  pile  for  the  water- jet.  For  experimental 
purposes  the  pipes  were  2,  ij,  ij  and  i  inch  in  diameter. 
The  piles  were  seasoned  from  30  to  41  days.  A  drop-hammer 
was  used  weighing  4700  pounds. 

"  After  moving  the  pile-driver,  the  usual  [work  preliminary 
to  the  actual]  driving  consisted  in  hooking  and  dragging  the 
pile;  lifting  it  to  place  and  attaching  the  hose,  or  attaching  the 
hose  first  and  then  lifting;  and  setting  the  pile  in  the  leads. 
The  water  was  then  turned  on  and  the  pile  usually  penetrated 
for  a  short  distance  without  the  hammer.  The  hammer  was 
then  placed  on  the  cap  and  the  pile  sank  further  to  a  depth 
depending  upon  the  nature  of  the  fill.  Next  the  hammer  was 
attached  to  the  pile  with  a  chain  and  the  churning  commenced. 
There  was  enough  play  in  the  chain  connection  to  give  about  a 
lo-inch  blow  of  the  hammer  each  time  the  pile  was  lifted.  When 
this  churning  became  ineffective  the  chain  was  disengaged  and 
the  pile  was  driven  with  blows  in  the  usual  manner." 

The  elementary  unit-times  were  obtained  in  sufficient  detail 
so  that  they  may  be  recombined  in  any  desired  arrangement. 
"This  enables  the  constants  to  be  distinguished  from  the 
variables,  abnormal  times  corrected,  and  lost  time  which  will 
not  occur  on  another  job  eliminated.  Allowance  can  be  readily 
made  for  the  time  which  is  always  necessarily  lost  during  rests 
and  ordinary  delays." 

The  average  time  per  pile  was  found  to  be  as  follows:  For 
moving  the  pile  driver,  29.0  minutes;  placing  the  pile,  23.0 
minutes  (including  delays  5.1  minutes);  driving  83.0  minutes 
(including  delays  2 1 .3  minutes) ;  a  total  of  2  hours  and  1 5  minutes. 
As  the  men  became  more  expert  in  moving  the  driver  and  plac- 
ing the  piles,  their  average  times  were  reduced  in  the  last  4 
days  to  27  and  13  minutes  respectively,  the  former,  however, 
being  still  unnecessarily  long  on  account  of  imperfect  rolls 
under  the  driver.  The  time  of  driving  was  greatly  increased 
by  the  low  pressure  of  the  water-jet.  Taking  an  average  for  16 
piles  driven  in  less  than  an  hour  each,  the  time  during  driving 
was  44  minutes,  making  the  total  i  hour  and  24  minutes.  Ex- 


ART.  50     .  ANALYSIS    OF   TIME   AND   COST  159 

pressed  as  percentages  the  three  operations  require  respectively 
32.1,  15.5  and  52.4  percent  of  the  total  time.  One-half  of 
the  delays  were  said  to  be  avoidable. 

A  further  analysis  of  the  time  required  to  get  ready  to  drive, 
exclusive  of  delays,  gives  the  following  percentages;  Attaching 
the  rope  to  the  pile,  14.1;  dragging  the  pile  to  the  driver,  30.4; 
attaching  hose  and  ropes  preparatory  to  raising  15.6;  rais- 
ing the  pile  to  a  vertical  position,  12.2;  placing  the  pile  in  the 
leads,  15.9;  and  placing  the  hammer  and  cap  on  the  head  of 
the  pile,  11.8. 

The  number  of  blows  of  the  hammer  varies  from  112  to 
1160,  the  average  being  589;  the  average  range  in  the  fall  of 
the  hammer  is  from  i.o  to  5.6  feet,  exclusive  of  i  range  from 
25  to  20  feet;  the  average  fall  for  the  last  blow  is  4.7  feet, 
exclusive  of  one  drop  of  10  feet;  while  the  average  penetration 
under  the  last  blow  is  closely  J  inch,  the  maximum  value  being 
|  inch.  The  total  penetration  varies  from  25.6  to  32.0  feet, 
exclusive  of  one  of  18  feet,  the  average  being  28.7  feet. 

The  same  investigators  made  the  analysis  of  the  cost  for 
making  and  driving  the  piles,  expressed  in  cents  per  linear  foot 
of  piling,  which  is  given  on  the  next  page.. 

Accordingly  the  total  cost  per  linear  foot  for  making  and 
driving  the  piles  is  $1.64.  The  cost  for  items  i  and  28  are 
based  on  the  assumption  that  the  plank  is  used  four  times. 
A  few  of  the  items,  such  as  12  and  13  are  constant  per  pile 
and  independent  of  the  length,  and  may  therefore  be  modified 
for  a  close  estimate.  The  only  items  depending  upon  the 
character  of  the  ground  are  22,  24,  25,  and  27.  The  cost  for 
these  items  is  based  on  the  assumption  of  driving  five  and 
three-fourths  piles  in  eight  hours,  and  hence  the  corresponding 
cost  can  be  estimated  for  a  harder  or  softer  ground  by  as- 
suming the  number  of  piles  to  be  driven  per  day. 

To  make  similar  records  of  value  for  other  estimates  the 
following  elements  must  be  kept  in  mind:  (i)  "To  distinguish 
between  the  times  which  are  constant  for  any  job  and  those 
which  vary  with  the  quantity  of  the  work;  (2)  to  separate  items 
which  may  be  abnormally  large  or  abnormally  small  on  the 


160  CONCRETE   PILES  CHAP.  IV 

1.  Plank  for  molding  platform 2 . 56 

2.  Lumber  for  chamfer 0.72 

3.  Spikes  for  platform  | 

4.  5.  Nails  (qd.  and  4d.)  for  forms   J 

6.  Crushed  stone. . 5.12 

7.  Sand i .  26 

8.  Cement 8.64 

9.  Longitudinal  reinforcing  bars 26 . 70 

10.  Lateral  reinforcing  loops 4.01 

11.  Wire  to  bind  reinforcement  together o.  50 

12.  Extra  short  bars  in  head o-  79 

13.  Nipples  for  jet  pipe o . 49 

14.  Ells  for  jet  pipe 0.39 

15.  Jet  pipe 3.46 

16.  Hooks  to  handle  pile 0.82 

17.  Bending  and  placing  reinforcement 8.38 

18.  Labor  on  pile  platform 2 . 26 

19.  Labor  on  forms 5.72 

20.  Labor  on  concrete 7.51 

21.  Superintendence  for  making  piles 2 . 13 

22.  Pile-driving  labor 27.22 

23.  Cutting  slot  in  tip  of  pile o.  20 

24.  Repairs  to  pile-driver  and  cap 1.52 

25.  Cutting  off  broken  piles i . 61 

26.  Rent  of  engine 2 .07 

27.  Superintendence  for  driving  piles 2 .86 


Cost  varying  with  number  and  length  of  piles. ....  117 .05 

28.  Plank  for  sides  of  forms $i  7 . 50 

29.  Plank  for  ends  of  forms 7 . 50 

30.  Pile-driver,  25  percent  of  cost 49-55 

31.  Getting  ready,  two  days 60.00 

32.  Teaming  for  pile-driver,  etc 34-55 

33.  Removing  driver 34  •  61 


Total  cost  for  the  job $203 . 71 

Cost  of  items  which  are  constant  for  each  job 13 .91 


Total  estimated  net  cost  per  linear  foot  if  the  job  has  48  piles    130 . 96 
Add  25  percent  for  pumping,  connections,  contingencies  and 

profit 32 . 74 

163.70 


ART.  51  FORMULAS   FOR  BEARING  POWER  l6l 

job  in  question,  so  that  allowance  may  be  made  for  these 
particular  items  in  future  estimates;  (3)  to  separate  the  time 
necessarily  wasted  because  of  abnormal  conditions,  or  because 
the  work  is  of  a  new  or  untried  character." 


ART.  51.     FORMULAS  FOR  BEARING  POWER 

In  Art.  27  a  reference  is  made  to  the  relation  between  the 
weights  of  the  hammer  and  pile.  The  formulas  for  the  bearing 
power  of  piles  given  in  Arts.  25,  26  and  30  do  not  take  this 
into  account  by  means  of  a  separate  term,  but  it  is  understood 
that  this  relation  must  be  considered  in  any  rational  use  of 
the  formulas. 

On  account  of  the  great  weight  of  concrete*  piles  this  relation 
becomes  one  of  increased  importance,  but  it  does  not  seem 
to  be  sufficiently  appreciated  in  practice.  Conservatism  tends 
to  employ  the  same  weight  of  hammers  for  concrete  piles  as 
for  timber  piles,  and  to  increase  these  weight  for  new  equip- 
ment but  slowly.  Progress  in  this  respect  may  be  materially 
aided  by  the  use  of  formulas  in  which  the  weight  of  the  pile 
is  introduced  separately.  Several  formulas  of  this  type  are 
in  extensive  use  in  Europe. 

EYTELWEIN'S  formula  in  its  ordinary  form  gives  the  ulti- 
mate resistance,  but  if  one-sixth  of  its  value  be  taken  as  in  the 
case  of  the  Engineering  News  formula,  it  becomes 

2WhH  ! 


in  which  the  Wh  denotes  the  weight  of  the  hammer,  W  P  that 
of  the  pile,  H  the  fall  in  feet,  and  s  the  average  final  penetra- 
tion in  inches.  It  will  be  noted  that  if  the  penetration  is  i 
inch,  and  the  hammer  and  pile  have  the  same  weight,  that  the 
value  of  the  denominator  is  the  same  as  if  it  were  j-f-i,  but  if 
the  hammer  weighs  twice  as  much  as  the  pile,  the  safe  load  is 
increased  33  percent.  If  the  penetration  be  f  inch,  the  bear- 
ing power  by  the  Engineering  News  formula  is  1.33  W\H, 


162  CONCRETE   PILES  CHAP.  IV 

whereas  formula  (i)  gives  2  WhH  and  2.67  WhH,  for  the  two 
cases  when  W  —  WP  and  Wh  =  2WP.  These  results  indicate 
such  radical  differences  that  an  urgent  need  is  shown  for  careful 
comparative  tests  for  driving  concrete  piles  with  different 
weights  of  hammers  and  within  a  limited  range  of  fall. 
RITTER'S  formula  may  be  written  in  the  following  form: 


Ultimate  load  =  ~  '  ~        +Wh+Wp          (2) 


in  which  the  terms  are  the  same  as  those  denned  in  the  preceding 
paragraph.  When  s=i  and  Wh  =  WP,  one-sixth  of  the  first 
term  has  the  same  value  as  the  Engineering  News  formula,  but 
when  Wh=  2WP  its  value  is  increased  33  percent.  This  formula 
differs  from  EYTELWEIN'S  for  the  ultimate  load  merely  in  the 
added  weights  of  hammer  and  pile. 

As  a  result  of  extensive  experience  by  the  Raymond  Con- 
crete Co.,  in  driving  heavy  collapsible  cores  for  cast-in-place 
concrete  piles  M.  M.  UPSON  states  that  the  Engineering  News 
formula  may  be  safely  used  to  determine  the  approximate 
bearing  power,  and  that  the  bearing  power  of  the  core  may  be 
applied  to  the  cast-in-place  pile  provided  that  the  compression 
of  the  soil  is  not  released  by  the  collapse  of  the  shell.  Steam- 
hammers  are  generally  employed,  the  heaviest  hammer  being 
used  for  the  longest  standard  core. 

It  has  been  truly  said  that  no  formula  for  pile  driving  can 
give  more  than  an  approximation  to  the  supporting  power  of 
the  special  pile  observed,  and  only  at  the  time  of  driving; 
but  with  an  intimate  knowledge  of  the  soil  conditions,  a  good 
formula  becomes  valuable,  and  considerable  money  can  often 
be  saved  by  its  proper  application.  In  this  manner  the  science 
of  pile  driving  can  influence  the  art.  The  peculiar  and  appar- 
ently erratic  variations  in  the  results  obtained  can  be  readily 
and  satisfactorily  explained  by  conditions  in  the  ground, 
but  they  prove  that  it  may  be  misleading  to  use  a  formula 
when  no  exploration  has  been  made  of  the  sub-surface  con- 
ditions at  the  site. 


ART.  52  CHOICE   OF   TYPE  163 

ART.  52.     CHOICE  OF  TYPE 

When  it  is  determined  in  any  given  case  that  the  use  of 
concrete  piles  is  justified  by  considerations  of  economy  in  which 
due  allowance  is  made  for  durability,  as  well  as  the  other 
elements  referred  to  in  Art.  41  and  the  conditions  at  the  site 
are  known  as  the  result  of  careful  explorations  of  the  ground 
(Art.  174),  the  next  question  is  to  decide  what  type  of  pile  is 
especially  adapted  to  these  conditions,  due  consideration  being 
given  to  the  certainty  of  securing  adequate  strength  at  reason- 
able cost. 

It  may  fairly  be  assumed  that  each  type  of  pile  has  some 
distinctive  advantages  which  are  adapted,  more  or  less  closely, 
to  certain  conditions  of  the  ground  where  piles  are  necessary. 
To  use  a  type  of  pile,  under  conditions  which  are  not  favorable, 
involves  either  an  economic  loss,  or  a  smaller  degree  of  security, 
or  both.  Naturally  some  types  may  be  applicable  to  a  wider 
range  of  conditions  than  others  and  it  is  the  duty  of  the  engineer 
to  study  each  situation  as  a  special  problem. 

When  piles  are  used  to  support  a  structure  above  open 
water,  as  in  pile  trestles,  wharves,  piers,  etc.,  they  are  required 
to  resist  flexure,  as  well  as  to  act  as  columns.  Pre-molded 
piles  are  the  only  ones  which  are  adapted  for  this  service;  and 
they  should  be  molded  without  taper,  at  least  for  that  part  of 
the  length,  whjch  is  not  in  the  ground.  If  the  piles  penetrate 
sand,  which  is  not  liable  to  scour,  that  portion  may  be  tapered, 
since  in  sand  the  supporting  power  is  almost  wholly  due  to 
friction.  If,  however,  the  sand  is  liable  to  scour,  or  if  adequate 
total  penetration  can  be  secured  to  furnish  the  necessary 
frictional  surface,  as  well  as  the  required  horizontal  reactions 
without  exceeding  the  safe  bearing  value  on  the  side  of  the 
pile,  then  a  pile  with  uniform  cross-section  should  be  used. 

In  ordinary  sand,  quicksand,, or  in  combinations  of  sand  with 
gravel  or  clay,  so  as  to  produce  a  porous  mass,  in  which  the 
water- jet  can  be  used  successfully,  the  pre-molded  pile  has 
special  advantages. 

When  a  pile  is  driven  through  soft  material  to  a  hard  sub- 


1 64  CONCRETE   PILES  CHAP.  IV 

stratum,  so  that  it  must  act  as  a  column,  it  must  be  reinforced, 
and  hence  frequently  the  pre-molded  pile  is  the  only  type  that 
can  be  used.  The  pile  should  be  uniform  throughout,  so  as  to 
have  a  large  bearing  area  in  the  harder  substratum.  Whether 
other  types  can  be  used,  depends  upon  the  nature  of  the  over- 
lying material.  If  any  stratum  contains  quicksand  or  other 
soft  material,  which  will  not  retain  its  form  until  the  pressure 
of  the  concrete  can  resist  the  external  pressure,  then  no  cast-in- 
place  pile  should  be  used,  which  does  not  leave  a  casing  in  the 
ground  which  can  retain  its  form  until  the  concrete  has  set. 
If  such  a  shell  or  casing  is  used,  it  should  also  have  uniform 
diameter,  so  as  to  secure  a  larger  bearing  area  at  the  foot,  than 
that  for  a  tapered  pile. 

If,  however,  the  overlying  material  is  of  such  a  nature  that 
it  will  retain  its  form  temporarily,  until  the  concrete  is  in 
place,  then  those  types  in  which  the  pipe  is  gradually  with- 
drawn may  be  used.  If  the  underlying  stratum  which  is  to  bear 
a  considerable  part  of  the  load  is  not  sharply  defined  on  its 
upper  surface,  it  may  be  desirable  to  increase  the  bearing  sur- 
face of  the  pile  by  means  of  an  enlarged  base.  The  method  of 
forming  the  pedestal  pile  requires  the  material  adjacent  to  the 
base  to  be  displaced  by  the  pressure  of  the  concrete  due  to 
ramming.  If  the  material  is  not  homogenous,  the  base  may  be 
unsymmetrical  about  the  vertical  axis,  and  thereby  produce  an 
eccentric  reaction  on  the  pile  column,  thus  causing  dangerous 
stresses  in  the  stem.  In  any  case,  when  the  load  is  mainly 
carried  to  its  foot,  the  pile  must  be  reinforced,  unless  the  over- 
lying material  affords  good  lateral  support,  and  there  should 
also  be  some  limiting  ratio  of  length  to  diameter. 

It  should  be  remembered  that  if  subsequent  to  the  installa- 
tion of  plain  concrete  piles,  the  adjacent  ground  is  subjected 
to  very  heavy  loading,  that  in  some  kinds  of  earth  like  stiff 
clay,  lateral  pressure  will  be  developed,  thereby  causing  serious 
bending  moments,  which  piles  without  longitudinal  reinforce- 
ment may  be  unable  to  resist  safely. 

If  for  example,  the  substratum  is  hard  clay  and  the  foot  of 
a  pile  of  uniform  section  does  not  afford  sufficient  bearing  area, 


ART.  52  CHOICE   OF   TYPE  165 

then  an  elarged  base  may  be  formed  by  a  tool  like  that  referred 
to  in  paragraph  17  of  Art.  45. 

When  the  ground  is  compressible  at  the  top  but  not  soft,  and 
gradually  increases  in  density  downward,  any  one  of  a  number 
of  different  types  may  be  employed,  provided  proper  precau- 
tions are  taken,  but  all  of  them  should  be  without  taper,  so 
that  proper  advantage  be  taken  of  the  greater  bearing  at  the 
foot  and  the  greater  frictional  resistance  of  the  lower  surface  of 
the  pile.  Pre-molded  piles  will  probably  require  the  use  of  the 
hammer,  as  well  as  the  jet,  or  if  conditions  on  adjacent  property 
do  not  permit  the  use  of  the  jet,  the  driving  may  be  done  by 
the  hammer  alone.  For  cast-in-place  piles,  the  necessary  pre- 
cautions relate  more  particularly  to  the  order  in  which  the  piles 
are  placed,  so  that  no  core  or  pipe  is  driven  for  another  pile 
within  a  prescribed  distance  of  any  one  during  the  setting  of  its 
cement  (see  Art.  46).  When  proper  consideration  is  given  to 
the  importance  of  this  matter,  the  relative  cost  of  driving  differ- 
ent types  of  piles  assumes  a  different  aspect.  Usually  the  eco- 
nomic relation  will  decide  the  choice  of  type  of  pile,  and  hence  it 
is  of  the  utmost  importance,  that  the  same  degree  of  security 
should  be  demanded  for  every  one,  so  far  as  this  is  practicable. 

When  the  ground  near  the  surface  is  not  quite  sufficient  to 
carry  directly  the  load  transmitted  by  a  wall  or  column,  with  the 
aid  of  a  spread  footing  or  when  it  costs  less  to  increase  its  bear- 
ing power  by  means  of  piles,  then  the  tapered  pile  of  short 
length  is  most  advantageous.  Whether  the  pre-molded  pile  or 
one  of  the  cast-in-place  piles  will  be  most  advantageous,  prob- 
ably depends  upon  similar  considerations  to  those  described 
in  the  preceding  paragraph. 

If  the  ground  consists  of  silt  or  alluvium  for  a  great  depth 
and  increasing  but  slowly  in  density  with  the  depth,  so  that  the 
bearing  power  depends  practically  all  on  skin  friction,  the  choice 
between  a  tapered  and  an  untapered  pile  depends  upon  two 
factors.  The  pile  with  a  uniform  section  has  a  slightly  larger 
superficial  area  for  a  given  volume,  the  greatest  difference 
being  practically  less  than  5  percent.  Such  a  pile  has  .the 
additional  advantage  of  having  a  larger  proportion  of  its  surface 


1 66  CONCRETE  PILES  CHAP.  IV 

in  the  lower  part  of  the  pile,  where  the  friction  is  slightly  greater. 
But  the  tapered  pile  has  a  larger  section  area  of  concrete  at  the 
top  to  transmit  the  load  and  that  may  govern  in  some  cases. 
As  the  load  is  gradually  transferred  to  the  surrounding  earth  in 
passing  downward  through  the  pile,  the  decreasing  section  area 
of  a  tapered  pile  makes  it  conform  more  closely  to  one  of  uni- 
form strength  throughout. 

If  the  ground  is  tough  and  leathery,  so  as  to  cause  upheaval 
when  adjacent  piles  are  driven,  it  would  be  disastrous  to  use 
some  types  of  cast-in-place  piles ;  but  so  far  as  form  is  concerned 
the  piles  should  not  have  any  taper. 

Sometimes  deep  beds  of  clay  require  pile  foundations  be- 
cause the  upper  stratum  becomes  soft  during  the  flood  season, 
while  during  the  most  favorable  time  for  construction,  the  clay 
is  so  hard  that  it  is  impracticable  to  drive  any  piles.  Under 
such  conditions,  a  satisfactory  solution  consists  in  excavating 
holes  by  means  of  an  earth  auger  of  the  proper  diameter,  and 
then  driving  a  pre-molded  pile  into  it,  so  as  to  fill  the  hole  so 
prefectly  that  the  surface  water  will  not  follow  down  the  pile. 

Although  some  type  of  concrete  pile  may  be  adapted  to 
nearly  all  kinds  of  earth,  there  are  limitations  imposed  that 
leave  a  field  of  usefulness  for  the  timber  pile.  Some  black 
marshy  land  will  carry  timber-pile  trestles  safely  but  nothing 
heavier  than  that.  Concrete-pile  trestles,  with  their  rein- 
forced-concrete  caps  and  slabs  require  the  strata  below  the 
top  to  contain  sand,  gravel  or  stiff  clay.  In  other  cases, 
combination  piles  are  used  to  reduce  the  load  as  well  as  the  cost 
(see  Art.  47). 

ART.  53.     EFFECT  OF  TAPER 

To  indicate  the  relative  properties  of  tapered  and  straight 
concrete  piles  let  the  following  example  be  considered.  Let 
the  tapered  piles  be  20  feet  long,  and  the  diameters  of  its 
head  and  foot  be  20  and  6  inches  respectively,  making  its  volume 
20.2  cubic  feet.  Let  a  straight  pile  be  taken  having  the  same 
length  and  volume;  its  diameter  is  therefore  13.6  inches.  In 
the  tapered  pile  44.5  percent  of  its  volume  is  in  the  uppermost 


ART.  53  EFFECT   OF   TAPER  167 

quarter  of  the  pile,  and  74.2  percent  in  its  upper  half;  while 
35.1  percent  of  its  available  surface  for  frictional  resistance 
is  in  the  top  quarter,  and  63.5  percent  in  the  upper  half  of  the 
pile.  Since  piles  are  frequently  spaced  3  feet  between  centers, 
let  it  be  assumed  that  the  compression  of  the  earth  surrounding 
a  pile,  which  diminishes  from  the  pile  outward  according  to 
some  law  depending  upon  the  nature  of  the  material,  be  equiva- 
lent to  a  uniform  compression,  limited  to  a  radius  of  1.5  feet  from 
the  center  of  the  pile.  Dividing  the  depth  into  four  quarters 
the  ratio  of  the  displacement  of  the  pile  to  the  corresponding 
volume  of  the  compressed  earth  is  accordingly  25.8  percent  for 
the  top  division  16.9  and  9.8  percent  for  the  next  two  divisions 
and  4.7  percent  for  the  lowest  division.  For  the  straight  pile 
the  corresponding  values  are  14.3  percent  for  each  division. 
The  proportions  of  the  total  frictional  area  of  the  tapered  pile 
are  35.1,  28.4,  21.6,  and  14.9  percent  in  the  four  divisions 
respectively,  while  those  for  the  straight  pile  are  each  25.0  per- 
cent. The  frictional  areas  of  the  tapered  and  straight  piles 
are  68.1  and  71.2  square  feet,  the  difference  being  a  little  less 
than  five  percent.  It  should  be  noted  especially  that  about 
45  per  cent,  of  the  total  equivalent  compression  of  the  earth 
was  expended  in  the  top  division,  and  very  nearly  75  percent 
in  the  upper  half  of  the  depth. 

It  may  be  considered  objectionable  to  adopt  a  large  taper 
since  the  compression  of  the  earth  is  thereby  made  a  maxi- 
mum near  the  surface  and  a  minimum  near  the  foot  of  the  pile 
which  is  contrary  to  the  fundamental  principle  of  pile  founda- 
tions; and  since  the  area  available  for  frictional  resistance  is 
reduced  near  the  foot  where  the  natural  compression  of  the 
earth  is  generally  the  greatest  and  most  useful.  It  should  be 
added  that  the  highly  compressed  and  loaded  area  near  the  head 
of  the  pile  may  have  its  supporting  power  reduced  by  subse- 
quent shallow  excavations  or  by  erosion  in  contiguous  areas. 
Probably  a  more  important  objection  to  a  large  taper  is  that 
an  increased  bearing  capacity  is  artificially  created  in  the  ground 
which  becomes  dissipated  in  time  as  the  pressures  are  dis- 
tributed through  a  larger  mass.  In  districts  subject  to  floods 


1 68  CONCRETE   PILES  CHAP.  IV 

the  bearing  power  of  the  ground  near  the  surface  is  at  least 
temporarily  reduced  and  if  a  large  percentage  of  the  load  is 
carried  by  the  ground  near  the  surface,  serious  settlement  is 
very  likely  to  result. 

.  It  should  be  remembered  that  in  driving  a  straight  pile  the 
compression  of  the  earth  is  done  at  the  tip  by  increments  as 
the  penetration  of  the  pile  increases;  on  the  other  hand  in 
driving  a  pile  with  a  large  taper  the  compression  thus  made  at 
the  tip  is  materially  smaller,  but  the  compression  is  con- 
tinuously increased  all  along  the  depth  of  penetration  while 
the  total  resistance  increases  to  its  final  maximum  value.  The 
tapered  pile,  however,  causes  less  displacement  or  disturbance 
of  the  texture  or  internal  arrangement  of  the  material  through 
which  it  is  driven  than  the  straight  pile. 

Experience  in  driving  concrete  piles  into  hard  clay  for  the 
foundations  of  the  Kentucky  and  Indiana  bridge  at  Louisville, 
in  1911,  led  to  a  change  in  the  taper  by  reducing  the  thickness 
of  the  head  from  20  to  14  inches,  leaving  the  thickness  of  the 
foot  the  same  as  before,  or  9  inches,  and  below  which  there  was 
a  pyramidal  point  9  inches  long.  The  piles  were  square  in 
cross-section  and  22  feet  long.  In  some  cases  5000  blows  had 
been  required  previously  for  the  25-foot  piles  with  the  larger 
taper  (see  fourth  paragraph  of  Art.  43). 

Various  tests  have  been  made  to  determine  the  effect  of 
taper  upon  the  resistance  of  a  pile.  In  a  test  at  Chicago  in 
1901  a  tapered  steel  core  and  an  oak  pile  both  20  feet  long  were 
driven  within  a  few  feet  of  each  other.  The  diameters  of  butt 
and  tip  were  18  and  6  inches  for  the  core;  12^  and  10  inches 
for  the  oak  pile.  With  a  22oo-pound  hammer  falling  25  feet, 
the  former  penetrated  an  average  of  i  inch  for  the  last  several 
blows,  and  the  latter  5^  inches.  The  volume  of  the  oak  pile 
is  67.5  pel  cent  of  that  of  the  steel  core. 

In  incompressible  but  plastic  clays  the  wedge  action  of 
tapered  piles  is  found  to  be  of  no  value  according  to  loading 
tests.  Extensive  experience  proves,  however,  that  concrete 
piles  with  a  large  taper  have  been  used  successfully  in  compress- 
ible ground  to  form  foundations  without  subsequent  appre- 


ART.  54  DRIVING  AND  LOADING  TEST  PILES  169 

ciable  settlement.  In  many  cases,  doubtless,  the  spread 
footing  would  have  been  a  more  appropriate  type  of  founda- 
tion. In  other  cases,  sand  piles  (Art.  58)  might  be  preferable, 
for  if  the  ground  is  to  receive  its  greatest  degree  of  compression 
near  the  surface,  it  would  apparently  be  a  more  economical 
arrangement  to  fill  the  conical  holes  made  by  the  tapered 
core  with  sand  since  sand  is  less  expensive  than  concrete,  and 
the  increased  bearing  power  of  the  ground  could  be  utilized 
equally  well  by  the  concrete  cap  or  footing  (see  Art.  150). 

The  following  experiment  is  very  instructive  regarding  the 
effect  of  taper.  A  concrete  pile  was  driven  to  a  total  penetra- 
tion of  26.5  feet,  the  diameters  at  the  surface  of  the  ground 
and  at  the  foot  being  18.6  and  8  inches  respectively.  The  safe 
load  was  computed  to  be  40.9  tons.  A  wooden  pile  was  driven 
to  a  total  penetration  of  24  feet,  the  diameters  at  the  surface 
and  at  the  foot  being  nf  and  9^  inches.  Its  safe  load  was 
computed  to  be  n.6  tons.  These  piles  were  both  driven  in 
dense  blue  clay.  They  were  subsequently  loaded  and  the  test 
loads  for  a  settlement  of  J  inch  in  each  case  were  44  and  32.1 
tons  respectively.  As  the  frictional  surfaces  are  92.4  and  67.2 
square  feet,  the  resistances  are  found  to  be  0.476  and  0.478 
tons  per  square  foot  respectively. 

No  definite  conclusion  can  be  stated  with  respect  to  the  effect 
of  taper  since  no  adequate  experimental  investigation  has  been 
made  of  the  subject.  Tests  are  needed  with  piles  of  the  same 
length  and  total  penetration  but  with  gradually  increasing 
tapers,  and  these  tests  should  be  repeated  in  several  typical 
kinds  of  earth.  It  is  also  desirable  to  have  some  sets  in  which 
the  volume  is  constant,  and  others  in  which  the  frictional 
surface  is  constant.  The  problem  involves  a  determination 
of  the  most  efficient  taper  to  secure  an  adequate  total  penetra- 
tion in  combination  with  a  maximum  frictional  carrying 
capacity  per  unit  of  surface  area. 

ART.  54.     DRIVING  AND  LOADING  TEST  PILES 

Concrete  piles  have  been  in  use  so  short  a  time  comparatively 
that  no  standard  practice  has  yet  been  developed  with  refer- 


170  CONCRETE  PILES  CHAP.  IV 

ence  to  the  allowed  settlement  of  test  piles  for  a  given  loading. 
It  may  be  desirable  therefore  to  state  a  few  examples  of  such 
specifications.  In  one  case  where  the  piles  were  to  be  driven 
through  materials  ranging  from  quicksand  to  stiff  clay,  two 
test  piles  were  required  for  each  pier,  the  settlement  in  seven 
days  under  a  load  of  60  tons  per  pile  being  limited  to  i  inch. 
In  another  case  test  piles  35  feet  long  were  not  to  settle  over  f 
inch  in  24  hours  under  a  load  of  40  tons.  The  building  code 
of  a  certain  city  states  that  the  allowable  load  on  concrete 
piles  shall  be  taken  as  one-half  of  the  load  which  shows  no  settle- 
ment for  24  hours,  and  a  total  settlement  not  to  exceed  o.oi 
inch  per  ton  of  test  load.  Still  another  specification  requires 
that  not  more  than  J-inch  settlement  shall  occur  on  any  one  of 
six  test  piles  for  a  building  foundation  under  a  load  of  40  tons 
each.  The  piles  varied  from  30  to  40  feet  in  length  and  pene- 
trated sandy  soil  underlaid  by  irregular  strata  of  soft  blue  clay 
alternating  with  strata  of  stiff  material.  A  load  of  25  tons  was 
assumed  for  the  design. 

In  1913  the  city  of  Chicago  required  that  for  cast-in-place 
piles,  test  loads  shall  be  applied  on  at  least  two  piles  in  different 
locations  and  as  directed  by  the  Commissioner  of  Buildings, 
not  less  than  three  piles  being  driven  at  each  location.  The 
pile  to  be  loaded  is  to  be  placed  first;  within  six  hours  a  second 
pile,  and  within  20  to  24  hours  a  third  pile,  are  to  be  placed  at 
distances  from  the  first  not  to  exceed  twice  the  greatest  diameter 
of  the  pile,  the  measurements  being  made  between  centers. 
The  tests  are  not  to  be  made  until  ten  days  after  the  placing 
of  those  which  are  to  be  loaded.  The  remainder  of  the  test 
is  to  be  the  same  as  for  pre-molded  piles.  In  order  to  be  certain 
that  the  kind  of  cast-in-place  pile  is  adapted  to  the  local  sub- 
terranean conditions  it  is  necessary  to  excavate  one  or  more 
piles.  In  some  cases  it  may  be  necessary  to  drive  steel  sheet- 
piling  around  it  to  exclude  the  ground  water  in  order  to  make 
the  excavation. 

Another  city  adopted  specifications  in  1913  for  the  test  piles 
of  a  bridge  foundation,  requiring  a  balanced  platform  to  be 
built  on  top  of  each  test  pile,  and  to  have  level  readings  taken 


ART.  54  DRIVING  AND   LOADING  TEST  PILES  17 1 

on  a  rod  set  on  a  steel  dowel  grouted  into  the  pile.  For  each 
test  nine  readings  are  required:  Before  the  platform  is  placed; 
immediately  after  a  30-ton  load  is  placed;  36  hours  after  this 
load  is  placed;  after  the  load  is  increased  to  40,  50,  and  60  tons 
respectively;  36  hours  after  the  load  is  increased  to  60  tons;  after 
the  load  is  reduced  to  30  tons;  and  immediately  after  the  entire 
load  and  platform  have  been  removed.  To  be  acceptable  the 
pile  is  not  to  show  a  settlement  exceeding  J  inch  between  the 
first  and  third  readings,  exceeding  f  inch  between  the  first  and 
seventh  readings,  or  exceeding  —  inch  between  the  first  and  ninth 
readings.  The  safe  load  is  to  be  taken  as  one-half  of  the  load 
which  causes  a  settlement  of  f  inch,  and  if  this  load  is  less  than 
that  originally  assumed  for  the  design,  additional  piles  are  to  be 
driven  so  as  to  make  the  combined  capacity  of  a  group  of 
piles  adequate  for  the  imposed  load. 

The  following  is  the  record  of  a  loading  test  for  a  concrete 
pile  in  pier  19  of  the  reinforced- concrete  viaduct  on  the  Pitts- 
burgh and  Lake  Erie  Railroad  referred  to  in  Art.  47.  The 
pile  was  26.2  feet  long  below  cut-off,  the  length  of  pre-molded 
pile  used  being  23  feet.  In  driving  the  casing  the  average 
penetration  under  the  last  five  blows  of  a  3ooo-pound  hammer, 
falling  15  feet,  was  0.45  inch.  The  loading  was  begun  at  7 
A.  M.  on  Sept.  6,  1912.  The  loads  in  tons  and  corresponding 
settlements  in  feet  are  as  follows:  18.5,0;  27.0,  0.003;  32.0, 
0.004;  35-0,  0.006;  38.5,  0.006;  45.0,  0.006;  52.0,  0.008;  57.0, 
0.008;  59.0,  0.008;  60,  0.013  (Sept.  7,  2  P.  M.);  60.325,  0.013; 
60.325,  0.013;  (Sept.  9,  8  A.M.).  After  removing  the  load 
two-thirds  of  the  settlement  was  recovered  leaving  a  permanent 
set  of  only  0.004  foot  or  0.05  inch.  A  test  well  8  feet  distant 
indicated  that  the  pile  penetrated  10  feet  of  cinder  fill,  5  feet 
of  dark  mud,  3  feet  of  sand,  4  feet  of  gravel,  3  feet  more  of 
sand,  while  its  foot  rested  on  another  stratum  of  gravel  which 
is  4  feet  deep. 

The  loading  tests  of  two  pre-molded  piles  driven  by  very 
heavy  drop-hammers  have  been  published.  One  was  driven  by 
a  7ooo-pound  hammer  to  a  depth  of  27  feet  2  inches  through  silt, 
sand,  and  gravel.  A  test  load  of  63  tons  caused  a  settlement 


172  CONCRETE  PILES  CHAP.  IV 

of  only  |  inch  at  the  end  of  2  weeks.  Another  pile  driven  by 
a  i2ooo-pound  hammer  to  a  total  penetration  of  30  feet,  upon 
being  loaded  with  a  weight  of  72  tons  showed  no  settlement  at 
the  end  of  6  months.  The  use  of  such  heavy  hammers  was 
referred  to  in  Art.  48. 

While  experience  has  shown  that  in  most  conditions  of  the 
ground  the  phenomena  of  pile  driving  give  a  fair  measure  of 
the  bearing  power,  there  are  others  to  which  this  statement  does 
not  apply.  Some  moist  clays  are  practically  incompressible 
but  being  plastic,  the  piles  displace  the  material  and  force  the 
surface  upward  elsewhere.  This  movement  may  be  so  small  as 
to  escape  observation  unless  levels  are  carefully  taken.  In 
such  a  case  the  loading  of  test  piles  will  reveal  the  true  condi- 
tions. For  example,  a  pile  required  30  blows  of  a  steam-hammer, 
having  a  striking  weight  of  3000  pounds  and  stroke  of  30  inches, 
to  produce  the  last  inch  of  penetration  while  the  total  pene- 
tration was  only  9  feet.  The  ground  was  "  ordinary  yellow  clay 
which  was  moist  but  not  wet,  and  fairly  solid."  Under  a 
load  of  20  tons  the  settlement  was  3!  inches;  for  25  tons,  5 
inches  increasing  to  5!  inches  the  next  morning;  and  for  35 
tons,  7  inches,  which  increased  to  7J-f  inches  the  following  morn- 
ing. In  subsequently  testing  a  group  of  four  piles  it  was  ob- 
served that  some  of  the  adjacent  unloaded  piles  also  sank  dur- 
ing the  progress  of  loading,  but  rose  after  the  maximum  load 
had  been  in  position  for  a  time.  Level  readings  taken  over  the 
whole  area  of  the  excavation  revealed  the  fact  that  the  volume 
of  clay  forced  upward  was  practically  equal  to  the  volume  of 
the  piles  beneath  the  surface.  These  tests  led  to  a  change  in 
the  type  of  foundation  adopted. 

ART.  55.     SPECIFICATIONS 

In  Art.  38  extracts  are  given  from  GREINER'S  Specifications 
which  relate  to  timber  piles;  the  following  paragraphs  are 
taken  from  the  same  source  and  relate  to  concrete  piles. 

88.  Concrete  piles,  when  reinforced  and  designed  so  that  they  may  be 
handled  and  driven  with  steam-hammers  in  the  same  manner  as  timber 


ART.  55  r  SPECIFICATIONS  173 

piles,  and  when  of  the  specified  quality  and  sizes  driven  to  refusal,  may  be 
subjected  to  a  maximum  load  not  in  excess  of  24  tons  when  used  for  rail- 
way bridges,  all  movable  spans,  arches  and  high  abutments,  and  30  tons 
when  used  for  other  foundations.  Concrete  piles  molded  in  place  without 
metal  reinforcement  should  not  be  used  in  water  or  ground  so  soft  as  not 
to  give  firm  lateral  support.  When  they  are  molded  in  a  strong  metal 
shell,  previously  driven  to  refusal  and  which  remains  in  place  after 
concrete  has  set,  the  safe  loads  when  piles  are  completely  embedded  in 
firm  earth  may  be  taken  the  same  as  specified  above  for  reinforced  piles. 
When  their  design  is  such  or  the  conditions  are  such  as  to  necessitate  the 
piles  being  jetted  down  instead  of  driven,  the  safe  load  should  be  not  more 
than  specified  above  or  more  than  one-quarter  of  the  failure  load  as  deter- 
mined by  actual  tests.  When  concrete  piles  act  as  columns  they  shall  be 
designed  as  columns. 

135.  Concrete  piles  shall  be  of  portland  cement  concrete  in  the  propor- 
tion of  i  cement,  2  sand  and  4  broken  stone,  varying  in  size  from  |  inch 
to  i  inch.  They  shall  be  constructed  strictly  in  accordance  with  the  plans 
but  when  their  construction  is  not  shown  thereon  they  shall  be  of  a  type 
suitable  for  the  conditions,  and  which  will  meet  with  the  approval  of  the 
engineer.  Their  minimum  diameter  at. tip  and  maximum  diameter  at 
butt  shall  be  same  as  specified  in  paragraph  133  for  timber  piles.  When 
driven  through  hard  ground  they  shall  be  shod  with  steel  points  of  approved 
design.  When  subjected  to  the  maximum  loads  specified  in  paragraph 
88  they  shall  go  to  rock  or  shall  have  an  average  penetration  under  each 
of  the  last  twenty  blows  of  a  steam-hammer  not  in  excess  of  that  deter- 
mined from  the  formula  S=WH/ 45000—0.1.  In  case  this  maximum 
penetration  cannot  be  obtained  without  injury  to  the  piles,  or  on  account 
of  the  impracticable  length  required,  the  number  of  piles  shall  be  in- 
creased until  the  load  on  each  shall  not  exceed  the  amount  indicated  in  the 
following  formula  for  piles  supporting  railway  bridges,  all  arches  and 
movable  spans. 

P_i.o6  WH 

JT  — — 

5-f-o.i 

For  other  structures  the  above  load  may  be  increased  25  percent.  When 
concrete  piles  are  jetted  in  place  they  shall  either  go  to  rock  or  to  a  solid 
stratum  in  which  case  they  shall  be  tested  with  steam-hammers  and  the 
set  and  loads  shall  not  be  greater  than  above  specified.  When  piles  are 
placed  by  other  means  than  by  hammers  and  jetting  and  when  they  are  of 
such  design  as  not  to  permit  of  them  being  driven  same  as  timber  piles,  the 
safe  loads  and  numbers  required  shall  be  determined  by  tests  to  failure 
as  directed  by  the  engineer,  the  expense  of  the  tests  to  be  borne  by  the 
contractor  and  included  in  his  cost. 


CHAPTER  V 
METAL  AND  SHEET  PILES 

ART.  56.    TUBULAR  PILES 

Some  of  the  problems  relating  to  underpinning  and  the 
foundations  of  buildings  in  New  York  City  led  to  the  intro- 
duction in  1901  of  a  patented  pile  which  consists  of  a  steel  pipe 
filled  with  either  plain  or  reinforced  concrete.  The  steel 
pipe  or  casing  can  be  of  any  diameter  of  which  pipe  and  well 
casings  are  manufactured,  but  the  most  usual  sizes  are  12  inches 
inside  diameter  and  9  inches  outside  diameter.  The  thickness 
varies  from  i  to  f  inch.  Since  in  underpinning  the  head  room 
is  generally  limited,  the  casings  are  designed  to  be  driven  in 
sections  from  5  to  20  feet  in  length.  The  ends  of  the  sections 
are  machined  so  as  to  be  truly  perpendicular  to  the  axis,  thus 
securing  a  true  alignment  of  the  pile,  and  a  uniform  bearing  of 
the  metal.  Inside  sleeves  are  provided  to  hold  the  sections 
together  and  they  have  a  driving  fit  in  the  pipe.  Means  are 
provided  to  prevent  the  sleeves  from  moving  under  the  blows 
of  the  hammer  while  driving  the  pipe,  and  their  length  is  not 
less  than  twice  the  inside  diameter  of  the  casing.  The  lowest 
section  bears  on  the  shoulder  of  a  hollow  conical  shoe  of  cast 
iron  or  steel  which  is  fitted  with  a  hole  for  a  water-jet,  if  re- 
quired. The  casing  is  driven  like  sheet  piles  with  a  steam-  or 
pneumatic  hammer,  usually  without  leads,  the  head  of  the 
casing  being  protected  by  a  cap.  In  some  ground,  especially 
in  sand,  the  casing  is  driven  without  a  shoe,  and  the  sand  is 
removed  through  the  pipe  as  the  driving  proceeds.  It  is  claimed 
that  such  a  pile  has  been  driven  to  a  depth  of  80  feet  with 
perfect  alignment. 

When  the  casing  has  been  driven,  a  hollow  steel  tube  of  con- 
siderable strength  is  thus  provided  which  is  then  filled  with 


ART.  56  TUBULAR  PILES  175 

concrete.  When  the  concrete  is  to  be  reinforced,  sleeves 
connected  to  the  casing  are  provided  which  hold  each  rein- 
forcing rod  in  place  without  any  lateral  play.  The  pile  is 
built  up  as  it  is  driven  down  and  if  any  material  length  projects 
above  the  ground  it  is  cut  off  and  used  on  another  pile.  Before 
the  pile  is  filled  with  concrete  an  electric  light  can  be  lowered 
to  ascertain  if  the  true  alignment  of  the  casing  has  been  main- 
tained. In  underpinning,  the  casing  is  often  forced  down  by 
means  of  a  hydraulic  or  a  screw  jack.  If  driven  into  soft  soil 
without  a  shoe  the  concrete  may  be  rammed  so  as  to  form 
a  bulbous  foot  to  increase  the  bearing  area. 

Experience  indicates  that  if  the  earth  surrounding  the  piles 
remains  undisturbed,  the  casings  may  last  for  many  years. 
These  pile  casings  are  not  good,  however,  when  exposed  to  the 
action  of  moving  water  or  air,  which  permits  the  thin  film  of 
oxide  forming  on  the  surface  of  the  metal  to  be  removed.  In 
designing  piles  careful  consideration  should  be  given  also  to  the 
probability  of  injury  due  to  electrolysis  and  methods  of  protec- 
tion against  it.  In  the  trade  the  casing  described  above  is 
known  as  the  Simmons  sectional  concrete  pile  casing.  Piles 
of  this  kind  have  been  used  up  to  85  feet  in  length. 

Fig.  56^  shows  a  wall  pier  of  a  1 2-story  office  and  loft  build- 
ing built  in  1912-13  in  New  York  City  in  which  three  tubular 
piles  support  a  wall  column  seated  on  an  I-beam  grillage. 
The  inside  diameter  of  the  steel  tubes  is  12  inches,  and  they 
are  spaced  2  feet  between  centers.  Additional  piles  are  driven 
between  the  clusters  to  carry  the  walls  between  columns.  Most 
of  the  interior  foundations  have  clusters  of  four  piles  spaced 
2  feet  apart.  All  the  tubes  are  made  in  two  sections,  connected 
by  a  cast-steel  inside  sleeve  tapered  slightly  at  the  ends  to 
make  a  driving  fit  and  provided  with  an  exterior  horizontal  rib 
in  the  middle  against  which  the  pipes  take  bearing.  The  rate  of 
driving  with  a  steel  hammer  varied  from  40  to  200  feet  in  one 
8-hour  shift.  They  penetrated  through  some  sand,  about  8  feet 
of  mud,  5  feet  of  hard  clay,  25  to  35  feet  of  fine  wet  sand  and 
gravel;  to  the  irregular  surface  of  the  rock  which  in  most  places 
was  overlaid  by  about  2  feet  of  hard-pan.  The  interior  of  the 


I76 


METAL   AND   SHEET   PILES 


CHAP.  V 


pipes  was  cleaned  out  every  5  to  20  feet  by  the  use  of  air  pressure 
at  150  pounds  per  square  inch  delivered  through  a  2\  inch 
pipe  without  a  nozzle,  and  which  blew  out  the  sand,  lumps  of 
clay,  and  ground  water  high  into  the  air.  From  one  to  five  2- 
inch  reinforcing  rods  were  set  with  a  clearance  of  about  i  inch 
from  the  pipe  and  driven  to  a  solid  bearing.  Their  tops  were 
also  arranged  to  bear  firmly  against  the  cast-iron  cap.  The 


T  Wall  Columns  ~\ 


PileDetail  Wall  Pier 

FIG.  560. — Tubular  Piles. 

concrete  filling  is  a  1-2-4  mixture,  and  the  piles  were  propor- 
tioned for  loads  of  from  56  to  80  tons  each.  The  stresses  allowed 
for  the  steel  and  concrete  are  4200  and  350  pounds  per  square 
inch  respectively.  The  section  areas  of  steel  vary  from  17.8 
to  30.2  square  inches  and  of  concrete  from  109.9  to  97-5  square 
inches.  A  light  framework  containing  templates  at  the  top  and 
bottom,  and  thoroughly  braced  was  used  to  secure  accurate 
location  and  alignment.  It  will  be  observed  that  the  de- 


ART.  56  TUBULAR  PILES  177 

tails  of  these  piles  differ  from  those  described  in  the  preced- 
ing paragraphs. 

If  the  cleaning  out  of  tubes  or  casings  during  the  process 
of  sinking  causes  trouble  in  the  settlement  of  adjacent  buildings, 
they  may  be  driven  to  a  firm  bearing  on  the  rock  or  hard-pan 
and  cleaned  afterward  by  the  dry-blow-out  process.  A  bag 
of  dry  cement  may  then  be  placed  in  the  bottom  and  the 
reinforcing  rods  placed  in  position.  The  casing  is  filled  with 
water  to  resist  any  external  pressure,  if  necessary,  and  after 
the  cement  has  set,  the  casing  may  be  pumped  out  and  filled 
with  concrete.  Sometimes  the  jet  which  aids  in  sinking  the  tube 
and  scouring  out  the  interior  is  immediately  afterward  con- 
nected to  a  tank  of  grout  under  air  pressure,  and  by  discharging 
it  at  the  bottom  the  grout  displaces  the  water  and  sediment  and 
makes  it  overflow.  If  a  pile  does  not  extend  to  rock,  but  is 
jacked  down  to  a  sufficient  penetration  in  sand  or  gravel,  the 
jack  is  applied  again  after  the  concrete  has  set,  in  order  to  force 
it  to  the  required  resistance.  Under  such  conditions,  a  pile 
may  sink  from  3  to  6  inches  further.  In  this  manner  there 
is  more  certainty  of  distributing  a  given  load  equally  among 
several  piles. 

In  one  instance  borings  showed  that  a  bed  of  quicksand  25 
feet  deep  overlaid  a  stratum  of  very  coarse  gravel  charged 
with  water  under  a  high  head.  After  an  8-inch  tube  was  driven 
down  until  it  rested  on  the  gravel  and  was  cleaned  out  with  a 
jet,  a  i-inch  pipe  perforated  at  the  bottom  for  2  feet  was  driven 
3  feet  into  the  gravel.  Grout  was  forced  through  the  pipe  to 
form  a  solid  footing  of  grouted  gravel  and  to  seal  the  tube 
which  was  then  pumped  out  and  filled  with  concrete.  A  test 
load  of  35  tons  caused  no  appreciable  settlement. 

The  diameter  of  tubular  piles  has  been  increased  considerably 
over  those  stated  in  this  article  for  use  in  underpinning  and  for 
some  other  suitable  conditions.  When  the  diameter  is  large 
enough  to  admit  a  workman  to  excavate  the  interior  by  hand 
they  are  generally  sunk  by  the  pneumatic  process.  The  larger 
sizes  are  preferably  regarded  as  pneumatic  caissons  rather 
than  pneumatic  piles.  For  further  details  see  Chap.  XVI. 


METAL   AND    SHEET   PILES 


CHAP.  V 


ART.  57.     DISK  AND  SCREW  PILES 

A  disk  pile  is  one  which  has  a  disk  attached  to  its  foot  to 
provide  a  larger  bearing  area.  Disk  piles  have  been  used  prin- 
cipally in  ocean  piers  and  wharves,  where  the  total  penetra- 
tion is  not  large  and  is  subject  to  more  or  less  variation.  The 
minimum  penetration  should  not  be  less  than  about  6  feet 
below  any  possible  scour.  The  disk  is  a  casting  which  con- 
sists of  a  horizontal  circular  plate,  stiffened  by  a  number  of 
radial  ribs  and  connected  to  a  central  hollow  stem,  as  shown 
in  Figs.  570  and  b.  The  former  illustrates  the  connection  of 


FIGS, 


a  and  6.  —  Two  Forms  of  Foot  of  Disk  Pile. 


the  disk  to  a  flanged  cast-iron  pipe  which  forms  the  body  of 
the  pile,  and  the  latter  the  connection  to  a  steel  pipe.  The 
upper  part  of  the  stem  is  cylindrical  while  the  lower  part  is 
conical  so  as  to  form  the  nozzle  of  a  water-jet  or  to  permit  a 
water-jet  pipe  to  pass  through  it.  Sometimes  the  ribs  on  the 
upper  side  of  the  disk  are  made  higher  than  the  lower  ones, 
their  edges  being  inclined  at  an  angle  of  45  degrees.  The 
disk  pile  can  be  used  only  in  sand  or  soft  material  which  permits 
sinking  by  the  water-jet.  If  some  material  is  encountered 
which  is  not  easily  displaced  by  the  jet  alone  the  pile  may  be 


ART.  57 


DISK   AND   SCREW   PILES 


179 


rotated  to  cause  the  ribs  to  act  as  cutters.  In  THEODORE 
COOPER'S  General  Specifications  for  Foundations  and  Sub- 
structures of  Highway  and  Electric  Railway  Bridges  is  given 
a  table  of  the  minimum  sizes  of  pipe  for  corresponding  diameters 
of  disks.  The  diameters  of  disks  range  from  1.75  to  4  feet, 
those  of  the  cast-iron  pipe  from  8  to  14  inches,  with  a  thickness 


FIG.  57<;. 


FIGS.  570?  and  e. 
Four  Forms  of  the  Foot  of  a  Screw  Pile. 


FIG.  57 f. 


of  f  to  i  inch,  and  of  the  steel  pipe  from  6  to  10  inches,  the  thick- 
ness being  f  inch  in  all  cases.  The  thickness  of  the  disk  plate, 
ribs  and  thickest  part  of  the  stem  are  not  to  be  above  ij  inches 
for  a  diameter  of  2  feet  or  less,  and  i|  inches  for  larger  di- 
ameters of  disk.  The  ends  of  the  cast-iron  pipe  sections  are 
to  be  machined  so  as  to  secure  perfect  alinement. 

A  screw  pile  is  one  which  has  a  broad-bladed  screw  attached 
to  its  foot  to  provide  a  larger  bearing  area.     The  use  of  the 


l8o  METAL   AND   SHEET   PILES  CHAP.  V 

screw  pile  is  similar  to  that  of  the  disk  pile.  The  form  of 
the  screw  casting  is  illustrated  in  Figs.  57^  to/.  The  pitch  of 
the  screw  varies  from  one-third  to  one-sixth  of  its  diameter, 
the  pitch  adopted  in  any  case  depending  upon  the  difficulty  of 
securing  penetration.  The  points  of  the  screws  are  also  varied, 
the  gimlet  point  being  suitable  for  gravel,  the  blunt  point  for 
sand,  the  hollow  conical  point  for  the  use  of  a  water- jet  in  sand 
and  gravel,  and  the  serrated  point  for  soft  rock  or  coral.  The 
dimensions  of  the  shaft  of  the  pile,  and  of  the  screw  and  its 
connections,  must  be  carefully  designed  to  resist  the  torsional 
strength  required  to  sink  the  pile  into  position.  In  one  case 
where  the  frictional  resistance  was  so  great  as  to  break  several 
piles  by  torsion,  it  was  discovered  that  by  discharging  a  water- 
jet  on  the  upper  surface  of  the  screw  blade  the  friction  was  re- 
duced so  that  the  sinking  could  be  accomplished  without  diffi- 
culty. After  using  the  jet  only  about  one- tenth  as  much  power 
was  needed  to  rotate  the  piles. 

Screw  piles  were  first  used  in  1838,  and  disk  piles  in  1856. 
They  are  unsuitable  for  deep  foundations  where  the  over- 
lying material  is  soft  or  liable  to  scour  since  it  is  impossible  to 
brace  the  piles  below  the  surface.  It  is  quite  probable  that 
in  future  reconstruction  these  types  will  be  replaced  by 
reinforced-concrete  piles. 

ART.  58.     SAND  PILES 

As  stated  in  Art.  2  short  timber  piles  are  sometimes  used 
to  compact  the  soil  and  thus  increase  its  bearing  power.  The 
same  result  may  be  accomplished  at  less  cost  by  withdrawing 
the  pile  as  soon  as  it  is  driven  and  filling  the  hole  with  sand. 
Such  piles  are  called  sand  piles.  They  can  be  placed  without 
regard  to  the  elevation  of  the  ground  water-level,  but  cannot 
be  used  if  there  is  any  danger  of  scour,  or  in  regions  subject  to 
earthquakes.  The  use  of  sand  columns  confined  in  wooden 
boxes  to  lower  great  weights  has  proved  that  they  will  sustain 
loads  while  developing  relatively  small  lateral  pressures.  In 
order  to  have  the  sand  pack  firmly,  it  should  be  moistened 


ART.  59  TIMBER   SHEET-PILING  l8l 

when  placed  in  the  holes  and  tamped.  In  case  there  is  a  slight 
settlement,  the  sand  will  readjust  itself  and  maintain  its 
stability.  The  method  of  consolidating  the  ground  by  ramming 
its  surface  and  mixing  sand  with  it  during  the  operation,  is  far 
less  effective  since  a  hard  crust  is  thus  produced  which  trans- 
mits the  pressure  only  to  a  very  short  distance  below  the 
surface.  This  difference  may  be  proved  by  applying  test  loads 
and  noting  the  settlement  under  a  time  test  extending  over  a 
month  at  least. 

The  'compressol  system'  is  somewhat  analogous  to  sand  piles 
in  first  forming  a  hole  and  then  filling  it  with  a  different  material. 
The  hole  is  made  by  a  heavy  conical  perforator  having  a  sharp 
point  which  is  successively  raised  and  dropped  until  the  hole 
reaches  a  hard  stratum.  If  the  compressed  earth  does  not  keep 
the  water  out,  the  hole  may  be  lined  with  clay  dumped  in 
after  each  fall  of  the  perforator.  Boulders  are  dropped  into 
the  hole  and  rammed  with  a  tamping  rammer  which  is  shaped 
like  a  cartridge,  thus  forming  a  layer  at  the  enlarged  bottom 
of  the  hole.  Concrete  is  then  deposited  in  batches  and  tamped 
in  the  same  way.  In  this  way  a  sort  of  rude  concrete  pillar  is 
formed.  The  system  was  originated  in  France  and  is  seldom 
used  in  this  country.  It  is  more  economical  to  use  concrete 
in  the  form  of  concrete  piles  as  described  in  the  previous  chapter. 

ART.  59.    TIMBER  SHEET-PILING 

Sheet-piling  consists  of  special  shapes  of  piles  driven  in  close 
contact  to  form  a  reasonably  tight  wall,  in  order  to  prevent 
the  leakage  of  water  and  soft  materials,  or  to  resist  the  lateral 
pressure  of  the  adjacent  ground.  Sheet  piles  are  made  of 
timber,  of  steel,  and  of  reinforced  concrete.  Sheet-piling  is 
to  be  distinguished  from  'sheeting'  which  is  set  in  place  or  driven 
as  the  excavation  proceeds,  as  in  trenches  or  open  wells.  Sheet- 
piling  is  driven  in  advance  of  and  usually  beyond  the  final  depth 
of  the  excavation. 

The  best  form  of  timber  sheet-piling  is  known  as  Wakefield 
sheet-piling  and  has  been  very  extensively  employed  in  this 


182 


METAL  AND   SHEET   PILES 


CHAP.  V 


country.     The  patents  secured  in  1887  and  1891  have  expired. 

It  consists  of  three  planks  fastened  together  so  as  to  form  a 

tongue  on  one  edge  and  a  groove  on  the  other  (see  Fig.  590). 

The  planks  are  connected  by  two  bolts  at  intervals  of  about  6 

feet,  while  spikes  are  used  at 
intermediate  points  about  18 
inches  apart.  It  has  been  cus- 
tomary to  use  J-inch  bolts  for 
planks  from  if  to  i\  inches 
thick,  and  f-inch  bolts  for 
planks  3  to  4  inches  thick. 
For  sheet  piles  made  of  i-inch 
boards,  f-inch  bolts  may  be 
T  used.  For  the  thin  boards  or 
planks,  the  tongue  is  made  if 
inches  longer  than  its  thickness, 
while  for  the  thickest  planks,  the 
length  is  the  same  as  the  thick- 
ness. The  usual  width  of  the 
planks  is  12  inches  except  for 
those  less  than  2  inches  thick. 
By  sizing  the  middle  planks  to 
a  uniform  thickness,  a  good  fit 
can  be  secured  between  the 
tongues  and  grooves. 

Experience  has  shown  that 
these  triple-lap  piles  are  stronger 
to  resist  driving  than  if  made 
of  a  single  stick,  this  being  due 
in  part  to  the  fact  that  cross- 
grain,  knots,  or  other  defects  in 


FIG.  5905. — Wakefield  or  Triple-lap 
Timber  Sheet-piling. 


the  three  planks  are  not  likely  to  be  located  at  the  same  part 
of  the  length;  and  that  some  defects  become  visible  and  lead 
to  the  rejection  of  a  plank  which  might  not  be  visible  in  a  single 
stick  of  the  same  total  thickness.  Other  advantages  of  this 
form  of  pile  are  the  absence  of  waste  in  forming  the  tongue  and 
groove,  and  less  tendency  to  warp  or  bend  before  they  are  driven. 


ART.  59 


TIMBER    SHEET-PILING 


Fig.  590  also  shows  how  corners  may  be  turned  at  a  right  angle 
by  bolting  and  spiking  a  tongue  to  the  face  of  a  pile  or  at  any 
other  angle  by  fastening  a  tongue  to  a  beveled  side.  It  also 
illustrates  how  the  foot  of  each  pile  is  beveled  on  both  faces, 
in  order  to  drive  plumb,  and  on  one  edge  so  as  to  keep  in  close 
contact  with  the  adjacent  one.  The  tongue  should  always 
be  kept  in  the  lead,  otherwise  gravel  or  stone  may  become 
wedged  in  the  groove,  and  damage  the  succeeding  pile.  If 
it  is  desired  to  drive  the  sheet-piling  each  way  from  the  corner, 


FIGS.  59&-£. — Sections  of  Timber  Sheet-piling. 

the  first  pile  should  be  constructed  with  a  tongue  on  both 
sides,  and  sharpened  so  as  to  drive  plumb  longitudinally  as 
well  as  laterally  with  respect  to  the  lines  of  piling.  The 
last  pile  in  the  center  is  constructed  of  the  proper  width  and 
acts  as  a  wedge  to  tighten  the  line  if  necessary.  When  the  sheet 
piling  is  to  be  driven  to  rock  bottom,  the  middle  plank  should 
be  cut  off  square  at  the  end,  so  that  water  will  not  readily  pass 
underneath  the  piling  along  the  rock  surface. 

Some  other  sections  of  sheet-piling  are  shown  in  Figs.  59  b-f. 
In  Fig.  596  a  single  row  of  ordinary  planks  are  driven  edge  to 
edge.  This  arrangement  cannot  be  used  if  it  is  necessary  to 
secure  a  water-tight  wall.  In  Fig.  59^  two  rows  of  planks  are 
placed  in  contact  and  breaking  joints.  Fig.  59^  shows  the 


184 


METAL  AND   SHEET  PILES 


CHAP.  V 


cross-section  of  a  sheet  pile  which  is  merely  a  plank  with  an 
ordinary  planed  tongue  and  groove.  In  Fig.  59^  the  plank  has 
a  groove  cut  on  both  edges  and  a  tongue  formed  by  nailing  a 
strip  or  spline  into  one  groove  to  form  a  tongue.  In  this 
case,  the  tongue  can  be  made  of  a  different  species  of  tough 
wood  like  maple  or  elm,  and  carefully  selected. 

Fig.  59/  gives   the  details  of  construction  for  timber  sheet- 
piling  4  inches  thick  according  to  the  standard  adopted  by  the 


FIG.  59/. — Details  of  Timber  Sheet-piling  with  Dovetail  Joints. 

Southern  Pacific  Company.  The  strips  nailed  to  the  planks 
are  beveled  to  form  a  dovetailed  tongue-and-groove  joint. 
Sheet-piling  built  up  in  a  similar  manner  is  sometimes  made  as 
thick  as  12  inches,  and  in  exceptional  cases  15  inches. 


ART.  60.     STEEL  SHEET-PILING 

On  account  of  the  difficulties  encountered  frequently  in 
driving  timber  sheet-piling  in  hard  ground  without  injury, 
and  the  large  amount  of  bracing  required  to  resist  earth  and 
water  pressure  during  excavation  and  construction,  an  effort 
was  made  naturally  to  devise  a  sheet-piling  of  greater  strength 
and  stiffness,  without  excessive  resistance  to  penetration.  The 


ART.  60  STEEL   SHEET-PILING  185 

need  of  this  was  emphasized  by  the  increasing  size  and  depth 
of  foundation  constructions,  and  the  difficulty  of  securing  water- 
tightness  in  quicksand.  Rolled  steel  sheet-piling  was  intro- 
duced to  meet  these  conditions.  The  use  of  standard  structural 
shapes  in  building  up  sheet  piles  gave  such  excellent  results  as 
to  demonstrate  the  commercial  success  of  steel  sheet-piling. 
The  first  form  of  this  class  was  employed  in  1901,  in  the  foun- 
dations of  the  Randolph  Street  bridge  in  Chicago  and  is  similar 
to  that  shown  in  Fig.  6oa.  Alternate  piles  consist  of  standard 
I-beams,  and  the  others  are  built  up  of  two  standard  channels 
bolted  together  with  pipe  separators.  The  design  is  based 
on  a  foreign  patent. 

The  next  step  forward  was  taken  during  the  following  year 
by  the  introduction  of  the  Friestedt  interlocking  channel-bar 
piling.  Each  alternate  pile  consists  of  a  standard  channel, 
while  each  of  the  others  is  built  up  by  riveting  two  Z-bars  to  a 
channel.  An  improved  form  known  as  the  symmetrical  inter- 
lock channel-bar  piling  is  also  manufactured  in  which  a  con- 
tinuous Z-bar  is  riveted  near  one  flange  of  every  channel,  and  a 
short  Z-bar  clip  is  riveted  near  the  other  flange  at  the  upper  end 
only.  This  arrangement  makes  every  pile  alike  and  preserves 
its  symmetrical  head  to  receive  the  blows  of  the  hammer 
(see  Fig.  6ob).  The  experimental  work  begun  by  LUTHER  P. 
FRIESTEDT  in  1899  which  led  to  his  patented  form,  and  his 
efforts  to  extend  its  use  by  others,  fairly  entitle  him  to  be  known 
as  pioneer  of  the  steel  sheet-piling  industry  in  this  country. 

Another  form  which  employs  a  standard  structural  shape 
was  placed  on  the  market  in  1908.  The  piling  consists  of  I- 
beams  which  are  locked  together  by  what  is  known  as  a  lock- 
ing bar.  This  bar  consists  of  a  small  I-beam  which,  by  extra 
passes  through  the  mill,  has  its  flanges  bent  into  hook  shapes 
as  shown  in  Fig.  6oc.  One  locking  bar  is  attached  to  each  beam 
at  the  mills  by  steel  wedges  and  then  the  beam  and  locking 
bar  are  driven  as  one  sheet  pile.  The  beams  differ  slightly 
from  the  ordinary  standard  in  having  the  outer  corners  of 
the  flanges  rounded. 

Another  class  of  steel  sheet  piles  includes  those  which  con- 


i86 


METAL   AND   SHEET   PILES 


CHAP.  V 


1 


;  i 

; 

SL 

IT 

Clip 


Clip- 


Clip 


FIGS.  6oa-h. — Sections  of  Steel  Sheet-piling. 


ART.  60  STEEL   SHEET-PILING  187 

sist  of  a  single  shape  formed  by  special  rolls.  Fig.  6od  shows 
a  section  of  what  is  known  as  United  States  sheet-piling.  At 
one  edge  of  the  web  is  a  flange  with  a  bulbous  section  and  at 
the  other  edge  is  an  open  or  slotted  cylindrical  flange.  This 
type  was  invented  some  years  before  the  Jackson  and  Friestedt 
types  but  did  not  come  into  commercial  use  until  a  few  years 
after  their  introduction.  The  smaller  flange  of  one  pile  enters 
easily  the  larger  curved  flange  of  the  next  one,  the  slot  being 
wide  enough  to  allow  a  considerable  change  in  the  direction 
of  the  web. 

The  Lackawanna  sheet-piling  introduced  in  1908,  is  also  a 
special  rolled  section  as  illustrated  in  Fig.  6oe.  Both  flanges 
are  alike,  the  section  being  symmetrical  with  respect  to  a 
central  transverse  plane.  The  diagram  shows  how  the  flanges 
of  adjacent  piles  engage  each  other  to  form  a  double  interlock. 
The  shorter  flanges  may  be  said  to  engage  like  hooks,  while 
the  larger  ones  act  like  guards.  Where  flexural  strength  is  of 
primary  importance,  the  web  is  curved  as  indicated  in  Fig.  6of. 
It  will  be  noticed  that  the  web  is  bent  until  a  considerable  por- 
tion of  its  width  touches  the  plane  which  is  tangent  to  the 
curved  flanges  of  the  adjajcent  piles.  A  large  bearing  surface 
against  supporting  timber  wales  is  thus  obtained. 

Corrugated  steel  sheet-piling  which  was  first  used  in  1907 
is  illustrated  in  Fig.  6og  and  permits  the  use  of  very  thin 
plates.  A  double  thickness  of  metal  is  provided  at  each  joint. 
The  width  of  sections  can  be  varied  to  suit  the  conditions  of 
driving  them.  Fig.  6oh  shows  sections  of  the  Gould  sheet  pile 
in  which  alternate  piles  are  standard  channels,  as  in  the  Frie- 
stedt type,  while  each  of  the  others  consist  of  a  channel  and  a 
plate  bolted  together  with  a  spacing  timber  between,  the 
timber  being  of  such  a  size  as  to  provide  for  the  interlock  at 
each  edge.  A  U-shaped  bent-plate  shoe  is  bolted  to  the  bottom 
of  each  combination  pile  to  protect  its  foot  during  driving. 
There  are  several  other  patented  forms  which  have  been  used 
to  a  limited  extent. 

The  general  method  of  forming  a  corner  pile  is  by  cutting 
an  ordinary  sheet  pile  longitudinally  into  two  halves,  and 


1 88  METAL  AND   SHEET  PILES  CHAP.  V 

then  riveting  them  to  a  structural  steel  angle.  In  some  cases 
a  sheet  pile  has  its  web  bent  to  a  curve  of  short  radius  to  form 
a  corner  pile.  At  the  junction  between  a  longitudinal  wall 
and  a  transverse  wall  on  one  side  of  it,  a  half  section  like 
that  used  at  a  corner  is  riveted  to  the  web  of  a  whole  section 
by  means  of  two  angles. 

It  will  be  observed  that  each  type  of  sheet-piling  has  inter- 
locking edges  to  prevent  a  pile  which  is  being  driven  from 
pulling  apart  from  the  one  driven  previously.  This  is  an  im- 
portant advantage  not  possessed  by  timber  sheet-piling.  The 
tensile  strength  of  the  interlock  enables  steel  sheet-piling  to  re- 
sist a  considerable  lateral  pressure  without  the  aid  of  transverse 
bracing.  In  the  construction  of  some  very  large  cofferdams 
it  has  been  possible  to  take  advantage  of  this  feature  by  con- 
structing a  row  of  pockets  to  be  filled  with  excavated  material 
so  as  to  avoid  the  use  of  transverse  bracing  in  the  large  interior 
area  (see  Art.  71).  The  direct  tensile  strength  of  interlock 
for  five  types  of  steel  sheet  piles  for  sections  weighing  approxi- 
mately 40  pounds  per  square  foot,  with  one  exception,  were 
found  by  tests  in  1908  to  be  9746,  7769,  3842,  3362,  and  1094 
pounds  per  linear  inch.  More  extended  tests  later  gave  values 
of  9584,  7271,  6060,  3569,  2252,  2022,  and  1502  pounds  per 
square  inch,  the  lowest  three  values  relating  to  fabricated 
sections. 

Not  only  do  the  different  types  of  steel-piling  vary  materially 
in  the  tensile  strength  of  the  interlock,  but  also  in  the  section 
modulus  which  measures  the  resistance  to  flexure  between  the 
horizontal  wales  or  the  frames  which  support  them  laterally,  as 
well  as  in  their  least  radii  of  gyration  which  indicate  the  re- 
sistance as  a  column  while  being  driven.  Each  type  is  usually 
manufactured  in  different  sizes  and  weights;  for  example,  the 
United  States  piling  has  two  sections  with  a  net  width  of  about 
12  inches  with  weights  of  35  and  40  pounds  per  linear  foot, 
and  a  small  section  about  6  inches  wide  weighing  1 1  pounds  per 
linear  foot.  All  the  types  permit  some  degree  of  flexibility  in 
the  interlock,  being  small  in  those  using  structural  shapes  and 
large  in  the  special  rolled  sections,  the  maximum  change  of 


ART.  6 1  CONCRETE   SHEET-PILING  189 

direction  toward  either  side  being  about  20  degrees.  This 
arrangement  permits  piling  to  be  driven  in  a  curved  line,  or 
to  avoid  boulders  encountered  in  a  proposed  line. 

Steel  sheet-piling  is  employed  in  cofferdam  construction, 
for  retaining  walls,  to  protect  adjacent  buildings  during  ex- 
cavation, to  line  shafts  in  quicksand,  to  line  open  wells  for 
building  piers,  as  well  as  for  'dams  and  other  hydraulic  con- 
structions. It  is  practically  used  for  the  same  purpose  as 
timber  sheet-piling  but  the  results  secured  by  it  are  much  more 
certain.  Only  one  wall  is  often  required  to  secure  water- 
tightness  which  would  require  two  walls  of  timber  sheet-piling 
under  the  same  conditions.  Single  lengths  of  steel  sheet 
piles  52  feet  long  have  been  successfully  driven  with  sec- 
tions having  a  weight  of  about  40  pounds  per  linear  foot. 
Spliced  lengths  of  75  feet  were  employed  in  the  cofferdam 
around  the  wreck  of  the  U.  S.  Battleship  Maine  in  Havana 
Harbor.  It  is  not  necessary  to  form  a  splice  by  bolting  or 
riveting  but  merely  to  abut  the  pieces  and  break  joints  with 
the  adjacent  piles.  Spliced  lengths  up  to  96  feet  have  been 
employed  in  exceptional  cases. 

Further  details  regarding  the  properties  and  uses  of  steel 
sheet-piling,  proposed  specifications  and  an  account  of  its 
historical  development,  may  be  found  in  a  paper  by  L.  R. 
GIFFORD  on  Steel  Sheeting  and  Sheet-piling,  and  its  elaborate 
discussion,  in  Trans.  Am.  Soc.  C.  E.,  vol.  64,  pages  441-525, 
Sept.,  1909. 

ART.  61.     CONCRETE  SHEET-PILING 

In  the  construction  of  piers  or  wharves  where  sheet-piling 
forms  a  part  of  the  permanent  structure,  reinforced-concrete 
sheet  piles  are  employed.  Sometimes  they  are  rectangular 
in  cross-section  and  are  driven  in  as  close  contact  as  possible, 
the  foot  being  beveled  on  one  edge  like  timber  sheet  piles.  The 
larger  sizes  have  tongues  and  grooves  on  the  edges,  the  sides  of 
the  grooves  being  splayed  so  as  to  engage  the  tongues  more 
easily.  Experience  shows  that  it  is  not  advisable  to  have  a 


190  METAL   AND   SHEET   PILES  CHAP.  V 

thickness  less  than  8  inches  when  a  tongue  and  groove  are  used, 
as  it  is  otherwise  difficult  to  obtain  the  requisite  strength  for 
these  details.  Another  plan  consists  in  forming  a  semi-circular 
groove  on  both  edges,  thus  forming  a  cylindrical  space  with  the 
adjacent  pile,  to  be  occupied  by  the  water-jet  pipe  during  sink- 
ing and  to  be  filled  afterward  with  grout. 

At  the  terminal  piers  at  Brunswick,  Ga.,  reinforced-concrete 
sheet  piles  18  inches  square  were  used  for  the  bulkhead  at  the 
basin.  They  were  45  feet  long,  beveled  at  the  foot  to  12  by 
1 8  inches  and  weighed  7  tons  each.  Four  f-inch  square  rein- 
forcing bars  extended  the  full  length,  and  for  the  lower  two-thirds 
of  the  length  two  ij-inch  bars  were  added  in  trussed  form  to 
help  in  resisting  the  maximum  bending  moment.  In  1910  at 
the  Norfolk  Navy  Yard  the  sheet  piles  were  1 8  by  24  inches  in 
section  with  tongue  and  groove,  and  55  feet  long.  The  most 
extensive  use  of  concrete  sheet-piling  up  to  that  date  occurred 
in  the  Galveston  causeway  begun  in  1909,  9808  piles  being  re- 
quired. They  were  10  by  18  inches  in  section,  grooved  on  both 
edges,  and  grouted  together  after  being  driven.  To  improve 
the  protection  of  the  reinforcing  rods,  it  is  desirable  to  place 
them  farther  from  the  surface  on  the  water  side  than  on  the 
other  side  of  a  pile. 

In  order  to  combine  the  tensile  strength  of  the  interlock  for 
steel  sheet-piling  with  the  freedom  from  corrosion  of  concrete 
piles,  sections  have  been  designed  in  which  a  steel  pile  is  cut 
longitudinally  through  the  web  and  these  halves  are  cast  into 
a  concrete  pile  on  opposite  edges.  After  the  piles  are  driven, 
the  grooves  containing  the  steel  interlock  are  cleaned  out  with 
a  jet  and  filled  with  grout.  Another  arrangement  consists  in 
making  a  combination  pile  by  enclosing  an  entire  steel  sheet 
pile  within  a  concrete  pile,  the  joints  being  grouted  in  a  similar 
manner  after  driving  the  piles. 

ART.  62.    DRIVING  SHEET-PILING 

The  construction  of  a  single  wall  of  timber  sheet-piling  is 
illustrated  in  Fig.  620.  Each  row  of  vertical  guide  piles  supports 


ART.  62  DRIVING  SHEET-PILING  191 

several  horizontal  timbers  called  'wales'  against  which  the  sheet- 
piling  is  driven.  An  outside  wale  is  usually  bolted  to  the  upper 
inside  wale  in  order  to  hold  the  sheet-piling  in  line.  It  will  be 
noticed  that  a  pair  of  short  leads  is  attached  in  front  of  the 
ordinary  fixed  leads  of  the  pile-driver  in  order  to  bring  the  ham- 
mer directly  over  the  line  of  sheet-piling.  The  light-weight 
steam-hammers  especially  designed  for  driving  sheet-piling 
give  the  best  service,  most  of  which  are  operated  without  any 
leads,  being  held  in  position  by  the  boom  of  a  derrick.  Nu- 
merous illustrations  and  descriptions  may  be  found  in  the 
catalogues  of  manufacturers.  They  will  drive  piles  to  a  greater 
depth,  and  without  brooming,  splitting,  or  other  injury.  To 
secure  a  good  job,  the  piling  must  be  very  carefully  driven. 
If  a  pile  is  injured  by  some  obstruction  in  driving,  it  is  generally 
better  to  replace  it  at  once,  than  to  attempt  some  other  means 
of  repairing  the  wall  to  make  it  water-tight.  In  case  sheet- 
piling  has  to  be  driven  through  a  shallow  deposit  of  silt  or  sand 
to  a  rock  bottom  and  it  is  desired  to  secure  a  close  fit  where  the 
bottom  is  not  level,  a  sheet  pile  may  be  sharpened  to  a  knife 
edge,  driven  until  the  edge  is  broomed  to  contact  throughout, 
then  pulled  up,  the  end  cut  to  the  proper  form  and  finally 
redriven.  After  all  the  sheet-piling  is  in  place,  the  hammer 
should  be  placed  on  each  pile  in  succession  to  secure  closer 
contact  with  the  rock  by  slight  brooming  at  the  foot. 

Timber  sheet-piling  is  sometimes  used  to  form  cofferdams 
for  piers,  and  is  left  in  place  as  a  protection  from  scour  around 
the  heads  of  the  bearing  piles  which  support  the  piers.  This 
was  done  on  some  of  the  piers  of  the  Vancouver  bridge  of  the 
Portland  and  Seattle  Railway.  Wakefield  sheet  piles  were 
built  up  to  a  maximum  length  of  68  feet.  In  order  to  secure 
the  necessary  penetration  through  the  sand  which  varied  from 
45  to  59  feet  below  the  cut-off,  the  sheet  piles  were  sunk  with 
the  aid  of  a  water-jet.  It  would  have  been  impossible  to  drive 
them  without  the  jet  aiding  the  steam-hammer. 

An  ingenious  arrangement  in  which  a  guide  or  pilot  tube  is 
utilized  both  as  a  water-jet  tube  and  as  a  guide  for  each  pile 
is  described  in  Engineering  News,  vol.  70,  page  552,  Sept.  18, 


IQ2  METAL  AND   SHEET  PILES  CHAP.  V 

1913.  The  tube  which  has  a  flattened  oval  section  engages  the 
groove  in  the  pile  already  driven  and  the  adjacent  groove  of 
the  pile  to  be  driven.  The  tube  is  afterward  withdrawn  and 
the  space  filled  with  a  hardwood  spline. 

Steel  sheet  piles  are  driven  generally  by  steam-hammers, 
the  weights  of  which  are  proportioned  to  that  of  the  piles  to  be 
driven.  The  double-acting  steam-hammer  is  very  effective  for 
this  purpose  on  account  of  its  rapidity  of  action  which  keeps 
the  pile  practically  in  constant  motion,  and  since  it  can  be 
handled  for  this  purpose  without  leads.  The  lightest  hammer 
of  several  designs  can  be  handled  by  one  man,  and  sometimes 
a  step  is  attached  to  the  hammer  frame,  so  that  the  weight  of 
the  man  who  operates  it  may  be  added  while  driving.  Long 
sheet  piles  with  heavy  sections  are  driven  with  heavy  steam 
hammers  and  pile-drivers. 

The  comparative  resistance  of  different  makes  of  steel  sheet- 
piling  is  indicated  by  driving  tests  with  five  types  of  piling  at 
Black  Rock  Harbor  in  1908.  The  number  of  blows  of  the 
steam-hammer  per  square  foot  of  piling  was  found  tp  be  13.9, 
14.4,  12. i,  19.6,  and  22.9.  All  of  the  piling  weighed  about  40 
pounds  per  square  foot,  except  one  type  which  was  lighter. 

To  protect  the  head  of  a  steel  sheet  pile,  especially  in  hard 
ground,  a  cap  is  generally  employed  which  contains  a  wooden 
cushion  or  driving  block.  Its  base  contains  grooves  or  sockets 
which  fit  over  the  pile.  The  elaborately  illustrated  catalogues 
of  manufacturers  of  steel  sheet-piling  show  plans  and  sections 
of  caps  which  are  designed  for  each  type  of  pile.  There  is 
usually  a  transverse  as  well  as  a  longitudinal  groove  in  the 
cap  so  as  to  fit  a  corner  pile  or  a  junction  pile  as  well. 

In  driving  through  material  with  a  large  proportion  of  sand 
or  clay,  the  interlocks  seal  themselves  with  the  material 
penetrated.  Occasionally  strips  of  wood  are  driven  into  the 
openings,  which  by  swelling  help  to  make  the  joint  water-tight 
above  the  bottom  of  the  water.  Sawdust  or  wood  pulp  may 
also  be  used  to  stop  leaks.  The  special  rolled  sections  offer  less 
resistance  to  driving  on  account  of  the  absence  of  rivets  or  bolt 
heads;  and  hence  they  may  also  be  pulled  more  easily.  In 


ART.  62  DRIVING   SHEET-PILING  193 

sections  like  the  United  States  piling,  the  bulbous  flange  should 
be  kept  in  the  lead.  Under  ordinary  conditions  steel  sheet- 
piling  may  be  pulled  and  redriven  a  number  of  times  and  finally 
has  considerable  scrap  value,  thus  frequently  making  the  cost 
less  than  for  timber  sheet-piling  which  can  ordinarily  be  used 
only  once.  Experience  has  shown  instances  in  which  steel  sheet 
piles  driven  into  hard  ground  could  not  be  used  over  again,  and 
in  exceptional  cases,  it  has  been  impossible  to  pull  it,  making 
it  necessary  to  dredge  away  some  material  alongside  and  to 
bend  it  down  on  the  bottom  to  avoid  interference  with  naviga- 
tion. Whether  this  result  was  due  in  any  measure  to  improper 
driving  remains  uncertain. 

Under  certain  conditions,  it  is  not  desirable  to  drive  each 
pile  to  its  full  penetration  at  one  operation.  In  order  to  main- 
tain good  alignment,  or  to  facilitate  closure,  it  is  often  advanta- 
geous to  set  up  a  considerable  number  of  sheet  piles  and  then 
drive  them  several  feet  at  a  time  in  succession,  repeating  the 
operation  until  the  desired  penetration  is  reached.  The  same 
method  of  driving  ahead  some  distance  may  be  used  successfully 
in  avoiding  injury  to  piles  when  boulders  are  encountered,  if 
they  are  not  too  large.  The  damage  thus  becomes  local  and 
limited  in  extent.  The  water-jet  may  also  be  used  to  aid  [ir> 
displacing  boulders.  Sheet  piles  should  be  carefully  handled, 
in  transportation,  for  with  a  small  clearance  in  the  interlock,  a 
bend  or  kink  due  to  careless  handling  may  cause  so  much  fric- 
tion that  the  pile  refuses  to  move  on  reaching  a  hard  stratum, 
and  may  result  in  crippling  the  pile,  if  driving  is  continued. 

Steel  sheet-piling  has  been  successfully  driven  through  sub- 
merged logs,  old  timber  cribs,  brick,  stone,  and  other  debris 
in  made  ground.  If  considerable  cribwork  or  logs  have  to  be 
penetrated,  it  may  be  more  economical  to  construct  a  special 
chisel  attached  to  the  end  of  a  timber,  and  to  cut  the  timbers 
with  the  aid  of  the  chisel  and  pile-hammer  before  inserting  the 
sheet  pile.  The  construction  of  such  a  tool  is  described  in 
Engineering  Record,  vol.  66,  page  704,  Dec.  21,  1912. 

To   drive  sheet-piling  below    the  leads  of  a  pile-driver,    a 
follower  may  be  constructed  for  the  purpose  by  riveting  to  the 
13 


IQ4  METAL  AND   SHEET  PILES  CHAP.  V 

web  of  a  piece  of  piling,  of  the  proper  length,  two  plates  or  chan- 
nels which  project  below  its  web  and  engage  that  of  the  sheet 
pile  to  be  driven. 

Steel  sheet-piling  may  ordinarily  be  pulled  up  by  means  of 
block  and  tackle.  If  difficulty  is  found  in  starting  a  pile,  it 
may  be  loosened  by  giving  ibseveral  blows  with  a  pile-hammer, 
or  by  using  a  pair  of  hydraulic  jacks,  one  on  each  side.  If  the 
piling  has  to  remain  in  place  for  a  long  time,  the  pulling  may  be 
facilitated  by  lubricating  the  joints  with  graphite  or  some  other 
material  which  will  prevent  corrosion  of  the  interlocking  joints. 
If  concrete  is  deposited  next  to  steel  sheet-piling,  which  is  to  be 
pulled  subsequently,  it  is  essential  to  prevent  contact  between 
the  concrete  and  steel  by  using  tar-paper,  or  preferably  light 
wooden  sheeting  with  tongue-and-groove  joints. 

Occasionally  it  is  necessary  to  cut  off  steel  sheet-piling  to 
an  exact  level.  Where  only  a  few  pieces  have  to  be  cut  and 
where  time  is  not  an  important  element,  hack  saws  may  be  used 
economically.  For  larger  quantities  to  be  cut  in  the  least  time, 
the  oxyacetylene  flame  is  the  most  advantageous  in  operation 
and  cost.  The  electric  arc  has  been  employed  in  some  instances, 
but  its  cost  is  very  high  and  it  is  difficult  to  handle  on  account 
of  the  intense  light  produced. 

ART.  63.    DESIGN  OF  SHEET-PILING 

When  sheet-piling  is  driven  a  short  distance  into  the  bottom 
and  is  supported  at  the  water  surface  by  wales  and  struts, 
as  illustrated  in  Fig.  63  a,  each  pile  may  properly  be  regarded 
as  a  simple  beam  with  a  span  d.  Taking  the  weight  of  a  cubic 
foot  of  water  as  62.4  pounds  and  expressing  distances  in  feet, 
let  a  sheet  pile  be  considered  i  foot  wide.  The  pressure  in 
pounds  per  square  foot  at  the  depth  d  is  62.4  d,  the  total  pres- 
sure on  the  pile  is  31.2  d2,  distributed  as  shown  in  Fig.  63  a; 
and  since  the  center  of  pressure  is  at  ^  d  from  the  bottom,  the 
horizontal  reaction  at  the  surface  is  10.4  d2.  By  the  principles 
of  mechanics,  the  bending  moment  at  any  distance  x  below  the 
surface  is  M=io.4  d2x  —  62.4 x  .  |  x  .  f  x=io.4d2  x—  10.4  x3. 


ART.  63 


DESIGN   OF    SHEET-PILING 


195 


Placing  the  first  differential  coefficient  dM/dx  equal  to  zero, 
there  is  found  x  =  d/  "^3  or  ^  dvr$=  0.577  ^>  f°r  the  location  of 
the  maximum  bending  moment.  The  maximum  bending  mo- 
ment is  accordingly  4.00  ds,  expressed  in  pound-feet;  or  48.00  d3, 
expressed  in  pound-inches.  If  the  total  pressure  be  regarded 
as  uniformly  distributed  over  the  pile,  the  value  of  the  maxi- 
mum bending  moment  is  3.90  d3,  or  2.5  percent  less  than  the 
true  value. 

The  strength  of  Wakefield  sheet-piling  must   be   regarded 
as  that  of  three  separate  planks  since  the  longitudinal  shear 


Water     Surface 


FIG.  630. 


FIG.  636. 


developed  between  them  by  flexure  cannot  be  fully  resisted  by 
the  bolts  or  spikes  which  connect  them.  Such  piles  are  analo- 
gous to  deepened  beams  which  also  require  better  means  than 
connecting  bolts  to  develop  their  strength  as  a  unit.  The  tests 
of  columns  composed  of  two  or  more  sticks  bolted  together  also 
show  that  in  no  case  is  the  resistance  materially  greater  than 
if  each  stick  were  acting  freely  (see  JACOBY'S  Structural  Details, 
Arts.  43,  45,  49  and  50).  Let  it  be  required  to  find  the  thick- 
ness of  Wakefield  sheet-piling  for  a  depth  of  water  of  10  feet, 
the  unit-stress  in  the  outer  fiber  being  taken  at  1000  pounds  per 


Ip6  METAL,  AND   SHEET   PILES  CHAP.  V 

square  inch.  The  resisting  moment  of  the  three  planks  1 2  inches 
wide  is  accordingly  1000  X  12  X  3/f/6  =  6ooo/2  pound-inches, 
in  which  /  is  the  thickness  of  each  plank  in  inches.  Equating 
this  to  the  bending  moment  of  48.ooX  io3  =  48  ooo  pound-inches, 
there  is  found  £=2.83  or  2!  inches.  In  determining  the  com- 
mercial sizes  required  account  must  be  taken  of  the  loss  due 
to  sawing  as  well  as  for  planing  the  middle  planks  in  the 
construction  of  sheet  piles. 

In  Fig.  63  b,  the  sheet  pile  is  horizontally  supported  at  the 
water  surface  and  at  an  intermediate  depth.  Let  d=i6  feet, 
and  c  =  6  feet.  The  pressure  at  a  depth  of  10  feet  is  624  pounds 
per  square  foot,  and  at  depth  of  16  feet  is  624+374.4  =  998.4 
pounds  per  square  foot.  Taking  a  width  of  pile  of  one  foot, 
the  pressures  on  its  lower  portion,  represented  respectively  by 
the  rectangle  and  triangle  of  the  shaded  area,  are  3744  and 
1123.2  pounds.  Treating  the  pile  as  a  simple  beam  with  a  span 
of  6  feet,  the  reaction  at  the  intermediate  wale  is  |X3744+ 
^X  1123.2  =  2246.2  pounds.  The  bending  moment  expressed 
in  pound-feet  at  a  distance  x  below  this  support  is  M  =  2246.4 
x  —(312  x2  — 10.4  #3).  In  the  same  manner  as  before  the  value 
of  x  which  makes  M  a  maximum  is  found  to  be  3.115  feet, 
while  the  value  of  the  maximum  bending  moment  is  3656.0 
pound-feet.  If  the  total  load  is  regarded  as  uniformly  dis- 
tributed, the  maximum  bending  moment  is  4867.2X3  =3650.4 
pound-feet  which  is  only  0.15  percent  less  than  the  true  value. 
Since  the  error  decreases  as  the  depth  d  increases,  it  is  suffi- 
ciently precise  for  purposes  of  design  to  use  the  simpler  approxi- 
mate method  of  'computation  for  all  portions  of  a  sheet  pile 
below  the  top  span,  for  which  the  true  value  of  the  maximum 
bending  moment  is  expressed  by  a  simple  term  as  given  in  the 
first  paragraph  of  this  article.  If  the  values  of  d  and  c  were 
16.25  and  6.25  feet  respectively,  the  approximate  value  of  the 
maximum  bending  moment  is  3999  pound-feet  which  is  prac- 
tically the  same  as  for  the  upper  span  of  10  feet. 

If  a  timber  sheet  pile  is  built  up  as  shown  in  Fig.  59 /,  the 
small  pieces  spiked  to  the  main  timber  to  form  the  tongue  and 
groove  should  be  omitted  in  computing  the  resisting  moment  of 


ART.  63  DESIGN   OF   SHEET-PILING  IQ7 

the  section.  The  values  of  the  section  modulus  for  the  com- 
mercial sizes  of  steel  sheet  piles  may  be  obtained  from  the  manu- 
facturers. The  corresponding  width  to  be  used  in  computing 
the  bending  moment  per  pile  is  the  distance  center  to  center  of 
interlock  when  assembled. 

The  design  of  sheet-piling  to  resist  earth  pressure  in  which 
the  material  has  more  or  less  cohesion  is  not  on  a  basis  that  is 
entirely  satisfactory.  The  conditions  vary  so  widely  and  often 
the  material  penetrated  in  any  locality  occurs  in  layers  of 
different  density  or  character  that  it  is  well  to  make  the  design 
so  as  to  be  on  the  safe  side.  Some  engineers  design  all  sheet- 
piling  for  hydrostatic  pressure,  increased  by  50  percent  or  more 
for  wet  slippery  material. 


CHAPTER  VI 
COFFERDAMS 

ART.  64.     THE  COFFERDAM  PROCESS 

When,  for  some  purpose,  it  is  desired  to  exclude  the  water 
and  expose  a  portion  of  the  bottom  of  a  river,  lake,  or  other 
body  of  water,  a  structure  called  a  cofferdam  is  employed. 
This  cofferdam  is  a  temporary  structure,  practically  water- 
tight and  large  enough  to  provide  adequate  room  for  working. 

Denned,  a  cofferdam  is  a  temporary  structure  used  for  the 
purpose  of  excluding  the  water  from  a  given  site,  or  area,  either 
wholly  or  to  such  a  degree  that  with  a  reasonable  amount  of 
pumping  the  permanent  substructure  may  be  built  within  it 
in  the  open  air,  or  that  other  work  may  be  accomplished. 

The  building  of  the  permanent  substructure  may  include 
pile  driving,  placing  grillages,  building  piers  and  abutments, 
etc.,  while  other  work  may  include  the  construction  of  dams, 
removal  of  sunken  vessels,  etc.  Where  the  ground  is  satu- 
rated with  water,  cofferdams  are  sometimes  used  in  placing 
foundations  for  buildings. 

Cofferdams  are  usually  built  in  place.  They  may  be  self- 
contained  or  may  depend  for  strength  on  the  natural  bottom, 
as  is  the  case  where  guide  piles  are  used.  Bracing  may  be  used 
to  resist  the  lateral  pressure  against  the  walls. 

To  obtain  water-tightness  the  sides  of  the  cofferdam  must 
be  tight  and  the  soil  on  which  the  cofferdam  rests  must  be 
impervious.  If  the  latter  condition  does  not  exist,  either 
the  sides  of  the  cofferdam  must  extend  through  the  pervious 
material  to  an  impervious  stratum  or  else  a  layer  of  concrete 
must  be  spread  over  the  bottom  inside  the  cofferdam  and 
allowed  to  harden  before  pumping  is  begun.  Absolute  water- 
tightness  is  seldom  sought,  it  being  cheaper  to  pump  a  moderate 

198 


ART.  65  EARTH   COFFERDAMS  199 

amount  of  leakage  than  to  go  to  the  heavy  expense  of  building 
a  structure  that  will  not  leak.  The  cofferdam  should  be  so 
designed  that  the  combined  cost  of  construction,  maintenance 
and  pumping  shall  be  a  minimum. 

To  depths  of  from  20  to  30  feet  the  cofferdam  process  will 
prove  the  best  and  cheapest  method  of  founding  bridge  piers 
and  abutments,  but  for  depths  greater  than  30  feet,  owing  to  the 
difficulty  of  properly  bracing  the  cofferdam  against  the  pressure 
of  the  water,  as  well  as  preventing  heavy  leakage,  some  other 
method  is  usually  preferable.  Cofferdams  over  50  feet  deep 
have  been  used  in  a  few  instances. 

Cofferdams  may  be  constructed  of  earth,  timber,  steel  or 
concrete.  They  may  be  divided  into  five  general  classes:  earth, 
sheet  pile,  crib,  movable  and  miscellaneous  cofferdams.  These 
classes  will  be  described  separately  in  the  following  articles. 

ART.  65.    EARTH  COFFERDAMS 

Of  the  five  classes  the  earth  cofferdam  is  the  oldest  in  origin 
and  simplest  in  construction.  Its  use  is  usually  limited  to 
shallow  water  with  low  velocities  of  current.  It  is  made  of  a 
bank  of  earth  placed  around  the  site  to  be  enclosed,  and  of  a 
thickness  sufficient  to  furnish  the  required  stability  and  to 
keep  the  leakage  down  to  a  small  amount.  The  earth  bank 
should  be  carried  up  2  or  3  feet  above  the  water-level  with  a 
width  of  at  least  3  feet  at  the  top,  and  with  side  slopes  corre- 
sponding to  the  natural  slope  of  the  material.  The  embankment 
should  preferably  be  composed  of  a  mixture  of  clay  and  sand  or 
gravel,  but  if  clay  is  scarce  the  bank  may  be  composed  of  sand 
with  a  clay  wall  in  the  center. 

The  amount  of  embankment  may  be  somewhat  reduced  by 
using  one  or  two  rows  of  sheet-piling,  in  which  case  the  cofferdam 
may  resemble  more  or  less  closely  the  sheet-pile  cofferdam 
described  in  later  articles.  As  to  whether  in  any  given  case  the 
cofferdam  should  be  classed  as  an  earth  or  sheet-pile  cofferdam 
will  depend  upon  whether  or  not  stability  and  water- tightness 
depend  primarily  upon  the  earth  filling. 


2OO  COFFERDAMS  t  CHAP.  VI 

Where  the  depth  of  water  is  not  more  than  4  or  5  feet  and  the 
velocity  of  the  current  would  wash  away  loose  material,  coffer- 
dams may  be  made  of  ordinary  canvas  bags  about  half  filled 
with  a  mixture  of  clay  and  sand.  It  is  important  that  the  bags 
shall  be  but  partially  filled  for  otherwise  they  will  not  pack 
together  closely. 

A  modern  and  up-to-date  use  of  the  earth  cofferdam  is  found 
in  the  construction  of  the  cofferdams  of  the  West  Neebish 
Channel  of  the  St.  Mary's  River.  In  some  places  the  depth  of 
the  water  was  far  too  great  for  the  economical  use  of  earth 
cofferdams  and  was  justified  here  only  by  the  extremely  favor- 
able conditions  that  obtained  for  placing  the  earth.  Two  sub- 
sidiary cofferdams  were  first  constructed  across  the  channel 
about  midway  between  the  main  ones  in  order  to  stop  the 
current  and  divert  the  flow  to  another  course.  1U These  tem- 
porary dams  were  about  1000  feet  apart  at  the  site  of  the 
channel  and  extended  across  the  river  from  the  mainland  to 
the  island,  varying  in  direction  to  suit  the  contours  of  the  river 
bed.  They  were  built  in  2  to  7  feet  of  water  flowing  3  to  6 
miles  an  hour.  The  construction  of  these  dams  stopped  the 
flow  of  water  in  the  West  Neebish  Channel  of  the  river,  that  the 
main  cofferdams  could  be  built  in  still  water,  and  also  laid  bare 
a  part  of  the  site  of  the  channel  about  1000  feet  long.  In 
building  these  temporary  dams,  which  varied  from  4  to  10  feet 
in  height,  broken  stone  and  rock  were  dumped  from  scows  on 
the  line  of  the  dams  until  the  force  of  the  current  was  broken 
and  the  rock  fill  carried  above  the  water.  Sandy  clay  was 
then  brought  in  and  dumped  on  the  upstream  side  of  these 
rock  embankments  in  order  to  silt  up  the  openings  and  pro- 
duce water-tight  dams." 

The  main  cofferdams  which  unwatered  the  86oo-foot  section 
of  the  work  were  structures  of  unusual  size.  The  upstream 
cofferdam  was  1900  feet  long  and  was  built  in  water  from  2  to 
18  feet  in  depth.  laThis  cofferdam  has  a  minimum  width  of 
8  feet  at  the  top,  which  is  7  feet  above  the  water,  and  has  side 
slopes  on  the  water  side  of  about  i  on  if,  and  of  about  i  on 

1  Engineering  Record,  vol.  56,  page  112,  Aug.  3,  1907. 


ART.  65 


EARTH   COFFERDAMS 


2OI 


2  on  the  other  side.  The  other  main  cofferdam  is  8600  feet 
downstream  from  this  one.  It  has  a  total  length  of  2600  feet, 
and  in  plan  is  arched  slightly  downstream  against  the  water  on 
that  side  of  it.  This  cofferdam  was  built  in  water  from  nothing 
to  26  feet  deep;  it  has  a  minimum  width  of  12  feet  at  the  top, 
which  is  6  feet  above  the  water;  its  side  toward  the  water  is 
built  on  an  average  slope  of  i  on  2,  and  the  one  on  the  other 
side  of  i  on  2^. 

"The  construction  of  the  upstream  main  cofferdam  was 
started  soon  after  the  current  of  the  river  had  been  broken  by 
the  temporary  dams.  Sandy  clay  and  mud  excavated  by  the 


El.  345.2-, 


s2xl2'Joists,2Q"c.  toe. 


I 


1   15    t'&e'o'c.toc.^         6 

(S'33 

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_„  .„       Filled  with 
6x8          Excavated  Material^ 

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fi; 
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a-  •••-••• 

fig           ? 

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-8\IO'                     W5? 

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r  About  ISO  'to 
Bottom  of  Excavathn 

Cross  Section 

FIG.  650. — Sheeting  for  Earth  Cofferdam  on  the  Ohio  River. 

dredges  at  work  on  the  adjacent  sections  of  the  channel  were 
brought  to  the  site  in  bottom-dump  scows  and  deposited  in 
place.  When  the  banks  thus  formed  had  been  carried  up 
until  the  bottom-Pump  scows  would  operate  no  longer,  the 
materials  were  loaded  on  flat-deck  scows,  and  handled  from 
these  to  place  in  the  embankment  by  a  clam-shell  bucket  on 
a  derrick  scow." 

French  engineers  have  made  extensive  use  of  the  earth 
cofferdam  for  work  on  their  various  canals.  In  some  work  on 
the  Meuse  Canal,  described  in  Annales  des  Fonts  et  Chaussees, 


202 


COFFERDAMS 


CHAP.  VI 


1896,  page  539,  gravel  ranging  in  size  from  about  i  to  4  inches — 
being  the  residue,  after  the  sand  was  used,  of  material  dredged 
from  the  canal  bottom — was  employed.  Water-tightness 
was  obtained  by  placing  a  layer  of  tan-bark  over  the  water 
face.  In  some  cases  the  head  of  water  on  the  cofferdam  was 
as  much  as  9  feet. 

In  place  of  earth,  cofferdams  are  sometimes  made  of  fascines. 
The  cofferdam  for  a  concrete  dam  at  Milford,  Conn.,  was  made 
by  forming  brush  into  mats,  which  were  sunk  by  loading  with 
rocks,  the  layers  of  brush  and  stone  alternating.  To  give  water- 
tightness  a  layer  of  earth  was  placed  over  the  upstream  side. 

Fig.  650  illustrates  the  cross-section  of  the  earth  cofferdam 
with  sheeting  used  in  the  construction  of  the  Ohio  River  Lock 


HeH  vertically  tyDtrrick  Boar 
S. 


FIG.  656. — Method  of  Constructing  Ohio  River  Cofferdam. 

and  Dam  48,  where  the  bottom  was  composed  of  sand.  To 
break  the  current  a  line  of  sheet-piling  was  first  driven.  Frames 
were  then  placed  by  a  boat  as  shown  in  Fig.  65^  and  connected 
to  the  sheet-piling.  Vertical  planking  was  placed  against  the 
frames  and  the  interior  then  filled  wirh  dredged  material. 
Gravel  was  placed  along  the  outside  of  the  sheet-piling  up  to  its 
top  and  on  a  slope  of  about  45  degrees;  the  space  between  the 
sheet-piling  'and  sheeting  was  also  filled  with  earth,  and  finally 
sand  was  placed  against  the  inside  wall  of  sheeting  up  to  the 
elevation  of  the  sheet-piling  tops.  This  sand  had  a  very  gentle 
slope,  running  approximately  100  feet  before  reaching  the  eleva- 
tion of  the  bottom  of  the  sheeting. 


ART.  66  WOODEN   SHEET-PILE   COFFERDAMS  203 

ART.  66.    WOODEN  SHEET-PILE  COFFERDAMS 

The  sheet-pile  type  may  be  considered  as  the  standard  form 
of  cofferdam.  It  consists  of  rows  of  sheet-piling,  usually  not 
more  than  two,  extending  around  the  site  to  be  enclosed.  The 
piling  is  held  in  place  in  various  ways  as  described  in  the  fol- 
lowing articles.  The  sheet-piling  serves  the  function  of  giving 
water-tightness  to  the  structure,  and  to  this  end  some  form 
of  intermeshing  or  interlocking  piling  is  always  employed. 
Strength  to  resist  the  pressure  of  the  water  outside  is  furnished 
by  guide  piles,  frames,  or  cribs,  in  addition  to  a  large  amount 
of  internal  bracing.  The  sheet-piling  may  be  of  wood  or  steel; 
at  the  present  time  (1914)  the  use  of  various  forms  of  steel  piling 
is  rapidly  increasing. 

Where  it  is  possible  to  drive  piles  some  distance  into  the 
soil  the  sheet-piling  is  best  supported  by  vertical  guide  piles 
and  horizontal  wales.  The  latter  will  not  only  furnish  a  guide 
for  the  sheet-piling  while  being  driven  but  will  also  add  strength 
to  the  cofferdam,  thus  decreasing  the  amount  of  internal  brac- 
ing necessary. 

DOUBLE  WALL  WITH  GUIDE  PILES. — Fig.  66a  shows  the  de- 
tails of  this  type  of  cofferdam.  It  is  composed  of  vertical 
guide  piles,  horizontal  waling  and  cap  timbers,  vertical  sheet 
piles  and  a  puddle  filling.  Rods  are  usually  put  in  near  the 
top  to  connect  each  pair  of  guide  piles  in  order  to  prevent  the 
filling  from  spreading  the  walls  apart.  If  the  top  of  the 
cofferdam  is  but  slightly  above  water-level,  struts  are  often 
placed  near  and  parallel  to  the  tie  rods,  serving  to  hold  the  two 
walls  apart. 

The  bearing  piles  are  driven  more  deeply  into  the  earth  than 
the  sheet  piles,  the  aim  being  to  drive  them  far  enough  to 
develop  the  full  transverse  strength  of  the  pile  when  acting  as 
a  free  cantilever  above  the  earth.  The  sheet-piling  should  be 
driven  to  a  fairly  impervious  stratum  to  prevent  leakage  under 
the  cofferdam.  The  space  between  the  walls  should  be  filled 
with  earth,  preferably  an  intimate  mixture  of  sand  and  clay  or 
gravel  and  clay,  to  form  a  puddle  (Art.  75),  which  will  mate- 


2O4  COFFERDAMS 

6  "x  12  "Sheet  Pile..,  ..-Strut  10  x  10  "        ^  „ 

4 

Drift  Bolt—  -\ 


•About  IZ  ft. 


Water 5urface\ 


•   P    u    d     d'  I  '  e.      '•   '•'"• 


CHAP.  VI 


-Cut  Washer 


7/t/&%8™'%fa*'"P«c+,  {BluetCtay,/////////' 


FIG.  66a. — Section  of  the  Double  Wall  of  a  Cofferdam  Showing  Puddle  Chamber. 


Rive 


?5'0"- *l 

rS/7rt/ce 

EI.+  IIO.O 


\0"*10"Y.P. 


El. +100.0 


L  ock 


ENG.  Ntws, 


Transverse      Section. 

FIG.  66fe. — Details  of  Double  Wall  of  Sheet-pile  Cofferdam,  Charles  River,  Boston, 

Mass. 


WOODEN    SHEET-PILE    COFFERDAMS 


205 


rially  assist  the  sheet-piling  in  making  the  cofferdam  water- 
tight. This  puddle  should  be  placed  in  thin  layers  and  thor- 
oughly tamped  in  a  damp  state.  Before  placing  the  same  it 
will  usually  be  advisable  to  dredge  out  the  soft  material  on 
the  bottom  to  an  impermeable  stratum.  This  puddle  filling, 
in  addition  to  promoting  water-tightness,  will  materially 
strengthen  the  structure.  Clay  is  often  banked  around  the 
outside  of  the  cofferdam  to  safeguard  it  further  against  leakage. 

The  cofferdam  should  have  its  puddle  chamber  wide  enough 
to  develop  the  required  strength,  furnish  water-tightness,  and 
afford  sufficient  space  for  plac- 
ing machinery,  gangways,  etc. 
One  rule  for  the  width  of  un- 
braced cofferdams  is  to  make 
it  equal  to  the  height  above  the 
ground  up  to  10  feet,  and  when 
the  height  is  greater  than  this, 
make  the  width  10  feet  plus 
one-third  the  height  in  excess 
of  10  feet.  The  design  of  sheet- 
piling  is  considered  in  Art.  63. 

A  well-designed  cofferdam  of 
the  double-wall  type  was  used 
in  the  construction  of  the  locks 
for  the  Charles  River  Dam, 
Boston,  Mass.,  where  the  length 
was  about  625  feet  and  the  width  about  250  feet,  surround- 
ing an  area  of  approximately  4  acres.  The  maximum  depth  of 
water  on  the  outside  at  low  water  was  20  feet.  As  shown  in 
Fig.  66  b  and  c,  the  cofferdam  consisted  of  two  rows  of  guide 
piles  ii  feet  apart,  with  piles  spaced  10  feet  on  centers,  which 
through  wales  supported  6 -inch  splined  and  grooved  sheet-piling. 

The  guide  piles  were  of  spruce,  45  feet  long,  and  each  alternate 
pile  was  braced  by  a  batter  or  spur  pile.  The  sheet-piling  was 
of  yellow  pine  with  spruce  splines  and  was  38  feet  in  length. 
The  remainder  of  the  details  are  clearly  shown  in  the  diagrams. 
A  filling  of  sand  and  clay  was  placed  around  both  the  inside  and 


206  COFFERDAMS  CHAP.  VI 

outside  of  the  cofferdam  as  well  as  in  the  puddle  chamber. 
On  the  inside  it  had  a  width  of  25  feet  at  the  top  and  then  sloped 
down  on  a  2  on  i  slope,  thus  making  virtually  a  combination 
pile  and  earth  cofferdam.  Although  probably  not  an  econom- 
ical form  of  cofferdam  for  ordinary  use,  yet  in  a  case  like  this 
where  the  filling  was  permanent  construction,  it  made  an  ad- 
mirable structure  to  withstand  the  37-foot  head,  which  was 
approximately  the  maximum  height  of  high  water  above  the 
bottom  of  the  lock  masonry. 

ART.  67.     SINGLE  WALL  WITH  GUIDE  PILES 

Where  the  space  available  for  the  cofferdam  is  restricted  or 
where  the  area  of  the  site  to  be  enclosed  is  small  and  the  head 
of  water  not  great,  a  cofferdam  having  a  single  wall  is  preferable 
to  the  double-wall  type.  Other  conditions  being  the  same  the 
former  type  will  require  more  bracing  than  the  latter,  but  in 
many  cases  this  will  prove  cheaper  than  the  extra  wall. 

Figs.  670  and  b  show  the  details  of  cofferdams  used  for  the 
rectangular  and  pivot  piers  for  the  Illinois  Central  Railroad 
bridge  across  the  Tennessee  River  at  Gilberstville,  Ky.,  both  of 
which  are  standard  types  for  single- wall  cofferdams  of  moderate 
size.  Before  placing  these  cofferdams  the  bottom  of  the  river 
was  dredged  down  to  about  17  feet  below  low  water  to  hard 
gravel.  Cofferdam  guide  piles  were  then  driven  and  ioX 
12-inch  wales  bolted  to  the  outside,  after  which  9Xi2-inch 
triple-lap  sheet-piling  was  driven  against  the  latter,  penetrating 
the  gravel  from  4  to  6  feet.  The  piers  were  founded  on  bearing 
piles  driven  from  16  to  20  feet  into  the  gravel  and  cut  off  2 
feet  above  the  bottom  before  the  cofferdam  was  placed. 

Before  pumping  out  the  water  a  3 -foot  layer  of  concrete  was 
placed  on  the  bottom,  thus  preventing  leakage  of  water  beneath 
the  cofferdam;  later  it  served  as  a  cap  for  the  bearing  piles. 
The  bracing,  which  is  clearly  shown  in  the  illustrations,  was 
placed  as  the  water  was  pumped  out.  The  octagonal  cofferdam 
was  braced  by  annular  trusses  which,  by  their  arch-like  action, 
proved  to  be  a  very  rigid  form  of  bracing,  and  yet  offered  no 


ART.  67 


SINGLE    WALL   WITH    GUIDE   PILES 


2O7 


B-J — i 


Cofferdam  for  Center  Pier  No. 3 


Half  Plan  of  Lower  Cofferdam  Half  Plan  of  Upper  Cofferdam. 

Cofferdam   for  Piers   4, 5  and  © 

FIG.  6;a. — Cofferdams  with  Single  Walls  of  Timber  Sheet  Piling  Supported  by 
Wales  and  Guide  Piles,  for  Piers  of  Illinois  Central  Railroad  Bridge  over  Tennessee 
River,  at  Gilbertsville,  Ky.  See  also  Fig.  620. 


208 


COFFERDAMS 


CHAP.  VI 


obstruction  to  the  work  of  building  the  piers/ which  were  of 
concrete.  The  forms  for  these  piers  were  braced  against  the 
trusses. 

A  good  example  of  a  very  large  and  high  single-wall  sheet- 
pile  cofferdam,  very  strongly  braced,  is  illustrated  in  Fig.  6yc, 
this  structure  being  used  to  found  the  pier  of  a  lift  bridge  for 


.............    ,  ITTJI  ffffTTTrmnmT 

•'  '     I     |'l     I       i      I  II  i i        !     M   I  !    Mil     I     I 

' ;  i     1 1  [  ]  i  j  |  j  1 1 1 1 1 1  n  1 1 ;  i  n ;  j  1 1!  1. 1 1 1  [  1 1 1  ii ;  1 1 


Section  A-)V 
lar  Coffe 


Rectangular  Cofferdam. 


%&? 


' 


Section  8-B. 
Octagonal  Cofferdam. 

FIG.  676.  —  Elevation  of  Cofferdam  Walls. 

the  Chicago  Terminal  Transfer  Railroad.  Two  sides  of  the 
cofferdam  were  on  land,  one  in  water,  and  the  other  two 
partly  in  water  and  partly  on  land. 

A  row  of  guide  piles,  from  6  to  8  feet  apart  and  40  feet  long, 
were  first  driven.  1  "  Six  tiers  of  inside  and  outside  waling  pieces 
were  bolted  to  these  piles,  and  on  the  land  side  370  6X1  2-inch 

1  Engineering  Record,  vol.  50,  page  636,  Nov.  26,  1904. 


ART.  67 


SINGLE    WALL   WITH    GUIDE    PILES 


209 


sheet  piles  34  feet  long  were  driven  between  the  outer  wales, 
and  6X i2-inch   horizontal  guide  pieces  at  the  surface  of  the 


ground  and  4  feet  below  it.  On  the  water  sides  274  34-foot 
Wakefield  piles  9  inches  thick,  made  of  3Xi2-inch  planks,  were 
driven  in  the  same  manner. 


210  COFFERDAMS  CHAP.  VI 

"The  piles  were  driven  as  the  excavation  progressed  inside  of 
the  cofferdam,  and  at  the  same  time  rows  of  transverse  and 
longitudinal  12X1 2-inch  horizontal  braces,  about  6  and  8  feet 
apart  on  centers  and  from  4  to  6  feet  apart  vertically,  were  set 
with  their  ends  engaging  the  round  piles  on  the  center  lines  of  the 
walls.  At  intersections  these  braces  were  supported  on  8X8- 
inch  vertical  timbers;  one  of  them  was  continuous  and  the  other 
was  cut  to  clear  it,  with  the  square  ends  abutting  against  the 
sides  of  the  first  piece  and  spliced  across  it  with  two  side  fish 
plates.  .  .  .  The  inside  wales  were  of  12X1 2-inch  timber 
(except  in  the  upper  two  tiers,  where  8X  1 6-inch  timber  was  used 
because  it  was  conveniently  available  from  the  contractor's 
stock),  all  of  them  being  lapped  and  halved  at  intersections. 
The  outside  wales  were  uniformly  6X12  inches.  The  round  pile 
caps  and  the  two  upper  rows  of  wales  on  the  water  side  were 
made  of  gX  i3-inch  timber.  All  wales  were  bolted  through  the 
round  piles,  and  the  oblique  joint  in  the  Wakefield  piling  was 
tied  by  bolts  through  both  faces. 

"In  the  longest  dimension  of  the  cofferdam,  the  six  tiers  of 
horizontal  struts  in  each  longitudinal  line  were  divided  into 
seven  panels  by  the  vertical  posts  supporting  them  at  the 
intersections  of  alternate  transverse  braces.  Each  panel  thus 
formed  on  three  of  the  long  lines  and  one  short  line  was 
X-braced  with  2Xio-inch  planks,  spiked  to  the  longitudinal 
struts  at  all  intersections  and  overlapping  in  the  centers  of  the 
panels,  as  shown  in  the  longitudinal  sectional  elevation.  Six 
lines  of  similar  bracing  were  provided  for  the  transverse  struts, 
but  varied  from  that  in  the  longitudinal  direction  in  that  the 
upper  and  lower  pieces  of  the  bracing  overlapped  each  other 
by  the  width  of  the  space  between  two  transverse  struts,  thus 
increasing  the  amount  of  bracing  and  the  rigidity  at  a  point  half 
way  between  the  top  and  bottom  of  the  cofferdam." 

ART.  68.    SHEET-PILING  SUPPORTED  BY  FRAMES 

Where  the  nature  of  the  bottom  is  such  that  piles  cannot 
penetrate  the  same  it  is  necessary  to  employ  a  frame  to  hold  the 


ART.  68 


SHEET-PILING   SUPPORTED  BY  FRAMES 


211 


sheet-piling  in  place.  These  frames  are  usually  built  on  shore, 
floated  to  the  site,  and  sunk.  Where  piers  are  to  be  built  under 
an  existing  bridge  it  is  sometimes  possible  to  suspend  the  frame 
from  the  bridge. 

SINGLE-WALL  TYPE. — At   the    site  of    the  bridge  piers  of 
the  Chicago,  Milwaukee  &  St.  Paul  Ry.  near  Kilbourn,  Wis., 


Sectional     Side     Elevation. 


FIG.  68a. — Cofferdam  for  Pier  of  Chicago,    Milwaukee,    and  St.   Paul    Railway, 

Kilbourn,  Wis. 

only  a  few  feet  of  sand  covered  the  rock  bottom  on  which  the 
piers  were  to  rest.  As  the  channel  was  narrow  and  the  current 
swift  it  was  essential  that  the  current  be  obstructed  as  little  as 
possible,  and  for  this  reason  the  single-wall  type  was  chosen  in 
preference  to  that  having  a  double  wall.  On  account  of  the 
slight  depth  of  sand,  guide  piles  could  not  be  used  and  so 


212  COFFERDAMS  CHAP.  VI 

recourse  was  had  to  a  frame.  As  shown  in  Fig.  68  a,  the  coffer- 
dam had  V-shaped  ends  to  diminish  the  force  of  the  current 
against  the  structure  and  was  held  in  place  by  wire  guys  an- 
chored to  the  rocks  on  the  sides  of  the  river.  The  frame,  the 
details  of  which  are  shown  in  the  illustration,  was  sunk  by  weight- 
ing with  scrap  rails.  The  covering  consisted  of  gXi2-inch 
Wakefield  sheet-piling;  in  driving  this  piling  care  was  taken 
to  broom  the  lower  ends  to  give  a  close  fit  to  the  irregular  rock 
surface. 

To  aid  in  giving  water- tightness  to  the  structure  canvas  was 
placed  around  the  outside  of  the  cofferdam,  and  was  so  arranged 
that  the  lower  part  rested  flat  on  the  river  bed  for  a  distance  of 
8  feet  out  from  the  dam,  while  the  upper  part  extended  above 
water-level.  The  lower  part  of  the  canvas  was  first  weighted 
down  with  iron  rails  and  sand  bags  to  make  it  fit  closely,  after 
which  about  fifty  car  loads  of  gravel  were  placed  upon  it.  As 
the  water  was  pumped  out  the  structure  was  thoroughly  braced 
as  shown,  but  on  building  the  pier  this  bracing  was  removed 
and  the  cofferdam  walls  braced  against  the  pier. 

One  of  the  largest  and  highest  cofferdams  ever  built  of  wood 
was  of  the  single- wall  sheet-pile-on-frame  type,  and  was  used 
for  the  Mare  Island  Dry  Dock  No.  2.  For  a  complete  descrip- 
tion of  this  structure  see  Engineering  Record,  vol.  57,  page  428, 
April  4,  1908. 

The  cofferdam  was  approximately  150  by  800  feet  in  plan  and 
the  maximum  head  of  water  on  it  was  48  feet.  The  framework 
and  bracing  consisted  of  five  horizontal  courses  of  transverse 
and  longitudinal  timbers,  the  timbers  of  each  course  being  con- 
nected to  those  of  the  adjacent  courses  by  posts,  the  whole  struc- 
ture being  built  as  one  unit  which  rested  on  bearing  piles 
previously  driven  and  sawed  off  under  water.  These  longitudi- 
nal and  transverse  rows  were  12  feet  apart  on  centers.  In  the 
bottom  course  all  timbers  were  16X16  inches  in  section,  while 
those  in  the  next  two  courses  were  14X14  inches,  with  12  X  12- 
inch  timbers  for  the  two  upper  courses.  The  rangers,  i.e., 
the  horizontal  pieces  forming  the  frame  proper  which  holds  the 
sheet-piling  in  position,  were  20X24  inches  in  section  for  the 


ART.  68  SHEET-PILING   SUPPORTED   BY  FRAMES  213 

bottom  course  and  12X12  inches  for  the  top  course,  the  other 
courses  having  intermediate  sizes  between  these  limits.  The 
distance  between  courses  was  approximately  10  feet.  In  addi- 
tion to  the  members  mentioned,  a  large  amount  of  bracing  in 
both  horizontal  and  vertical  planes  was  used. 

The  sheet-piling  units  were  formed  of  two  12  X 1 2-inch  timbers 
fastened  together  side  by  side  and  were  60  feet  long,  this  length 
being  obtained  by  using  two  pieces,  one  34  and  the  other  26 
feet  long.  A  tongue-and-groove  joint  was  made  by  spiking  to 
each  piece  of  piling  three  3  X4-inch  sticks,  two  on  one  side  and 
one  on  the  other,  thus  making  each  piling  unit  30  inches  wide. 
To  give  additional  water-tightness  to  the  cofferdam  a  large 
amount  of  filling  was  banked  around  the  outside. 

DOUBLE-WALL  TYPE. — This  is  a  form  but  little  used  since  it 
offers  but  slight  advantages  over  the  single- wall  type  and  is  con- 
siderably more  expensive.  It  is  more  easily  made  water-tight 
than  the  single- wall  form,  but  on  the  other  hand,  it  is  very  little 
stronger  because  strength  is  almost  entirely  dependent  on  the 
amount  of  internal  bracing  used.  Where  strength  must  be 
obtained  without  the  use  of  bracing  the  type  described  in 
Art.  69  should  be  used. 

The  cofferdams  for  one  of  the  piers  of  the  Chattahoochee 
River  Viaduct  had  an  inside  framework,  39  feet  long  by  15 
feet  wide,  which  was  composed  of  horizontal  frames  of  6X8- 
inch  pine  timber  braced  with  one  set  of  longitudinal  and  two 
sets  of  transverse  timbers.  These  frames  were  spaced  from  2 
feet  center  to  center  on  the  bottom  to  3  feet  centers  at  the  top 
and  were  held  in  place  by  vertical  posts  between  them,  the  total 
height  of  the  framework  being  9  feet.  The  outside  frames 
were  sufficiently  large  for  a  4-foot  thickness  of  puddle  and 
were  connected  to  the  inside  frames  by  braces  and  rods.  The 
framing  was  partly  built  on  shore,  launched,  floated  to  place 
and  there  completed. 

The  bottom  of  the  river  had  a  seamy  ledge  covered  with  a 
layer  of  sand  varying  in  depth  from  6  inches  to  3  feet.  As 
soon  as  the  framework  was  sunk  two  rows  of  sheet-piling,  each 
row  consisting  of  a  double  thickness  of  2-inch  pine  plank, 


214  COFFERDAMS  CHAP.  VI 

were  driven,  care  being  taken  to  break  joints.  The  bottom  of 
the  puddle  chamber  was  then  covered  with  two  layers  of  sacks 
loosely  filled  with  sand,  after  which  the  remainder  of  the 
chamber  was  filled  with  clay  puddle.  Considerable  trouble 
was  caused  by  water  coming  up  in  the  cofferdam  through  the 
seamy  ledge  and  this  leakage  was  stopped  only  after  a  2-foot 
layer  of  concrete  was  deposited  through  the  water  and  allowed 
to  harden  before  pumping  out  the  water. 

ART.  69.     SHEET-PILING  SUPPORTED  BY  CRIBS 

For  cofferdams  which  rest  on  hard  bottom  and  are  too  large  to 
employ  internal  bracing  economically,  a  series  of  cribs,  laid  up 
log-house  fashion,  are  used  to  hold  the  sheet-piling  in  place. 
Each  crib  unit  is  made  as  long  as  can  be  conveniently  handled 
and  as  wide  as  is  necessary  to  develop  the  required  stability. 
Rough  logs  are  generally  used  although  in  some  cases  they  may 
be  squared,  but  the  latter  offer  only  a  slight  advantage  over  the 
former.  In  building  these  cribs  the  bottom  courses  are  usually 
started  on  land  and  the  crib  is  built  to  a  height  sufficient  to 
permit  the  top  part  being  well  out  of  water  when  it  is  first 
launched;  after  this  it  is  launched,  floated  to  place  and  com- 
pleted. Where  the  stream  is  low  at  certain  times  of  the  year 
the  cribs  may  sometimes  be  built  in  place.  The  bottom  of  each 
crib  should  be  shaped  to  fit  the  rock  bottom,  and  if  a  few  feet 
of  sand  or  other  material  overlies  the  bedrock  this  should 
be  dredged  out  before  placing  the  cribs.  A  part  of  the  bot- 
tom of  the  crib  is  usually  floored  to  permit  placing  stones  so  as 
to  sink  it. 

After  all  the  cribs  are  sunk  the  remainder  of  the  space  inside 
of  them  may  be  filled  with  stones  or  earth.  The  latter  material 
possesses  the  advantage  of  not  only  giving  the  cribs  great  sta- 
bility but  also  to  secure  water-tightness.  After  the  cribs 
are  placed  sheet  piling  is  driven  around  the  outside  and  banked 
with  earth.  This  type  of  cofferdam  is  very  widely  used  in  build- 
ing dams  for  hydro-electric  plants. 

Fig.  690  shows  a  view  of  the  cofferdam  employed  in  the  con- 


ART.  69 


SHEET-PILING   SUPPORTED   BY   CRIBS 


215 


struction  of  a  dam  for  the  Connecticut  River  Power  Co.,  near 
Vernon,  Vt.  The  width  varied  with  the  height  of  the  coffer- 
,dam;  for  the  upstream  one  the  maximum  width  was  35  feet, 
while  the  maximum  height  was  42  feet,  or  16  feet  above  normal 
water-level.  The  structure  was  of  the  rock-filled  type  made  of 
round  logs  in  7-foot  checks,  with  the  face  logs  slabbed  on  the 
sides  to  give  good  bearing  for  the  sheet-piling.  The  top  of  the 
cribs  were  floored  with  logs  to  serve  as  a  walk  and  also  as  a 
protection  against  ice  pressures.  On  the  outside  the  cribs  were 
sheet-piled  with  3-inch  spline-and-grooved  spruce,  and  this  in 
turn  was  banked  with  earth  up  to  normal  water-level. 


k ••- 


4610 
Section   C~D. 

FIG.  696. — Typical  Section  of  Crib  Cofferdam.     Niagara  Power  Plant,  Electrical 
Development  Company  of  Ontario. 

The  cofferdams  for  the  Niagara  Power  Plant  of  the  Electric 
Development  Co.  of  Ontario  furnish  an  example  of  exceedingly 
strong  and  rigid  cofferdams  placed  under  the  most  trying 
conditions.  In  some  places  the  current  had  a  velocity  as 
high  as  17  feet  per  second  which  made  it  difficult  to  study  the 
nature  of  the  bottom  and  the  depth  of  water  previously  to 
placing  the  cofferdams. 

The  widest  part  of  the  cofferdam  consisted  of  two  lines  of 
parallel,  rock-filled  timber  cribs  with  a  space  between,  sheet- 
piled  and  filled  with  puddle  as  shown  in  Fig.  696.  Both  cribs 


2l6  COFFERDAMS  CHAP.  VI 

were  built  of  squared  timber  with  the  outside  wall  of  the  outer 
crib  laid  solid.  The  width  of  the  cribs  varied  to  meet  the 
variation  in  depth  and  the  bottom  of  the  cribs  was  made  to  fit 
the  irregularities  of  the  rock  surface.  In  shallow  water  the 
cribs  were  built  in  place  but  elsewhere  they  were  constructed 
in  the  river  upstream,  and  by  means  of  cables  from  the  shore 
they  were  floated  into  place  and  were  sunk  by  filling  with  rocks 
the  wells  which  had  bottoms.  For  further  details  of  this  in- 
teresting cofferdam  the  reader  is  referred  to  Engineering  News, 
vol.  54,  page  561,  Nov.  30,  1905. 

ART.  70.     STEEL  SHEET-PILE  COFFERDAMS 

The  advantages  which  steel  sheet-piling  possesses  over  the 
wooden  type  are  discussed  in  Art.  60.  On  account  of  these 
advantages  steel-piling  is  being  used  more  and  more  in  coffer- 
dam work.  The  details  of  the  structures  differ  but  little  from 
those  using  timber  sheet-piling,  the  main  difference  being 
that  the  steel  type,  on  account  of  the  greater  strength  and 
positive  interlock  of  the  piling,  requires  less  bracing. 

Fig.  joa  indicates  a  good  example  of  a  steel  sheet-pile  coffer- 
dam with  guide  piles.  In  the  illustration  the  guide  piles 
and  the  outer  course  of  wales  are  not  shown,  however.  The 
bottom  at  the  site  of  the  pier  consisted  of  hard-pan  to  an  un- 
known depth  covered  with  about  6  inches  of  mud.  The 
depth  of  water  was  about  9  feet  at  mean  tide,  which  had  a 
rise  and  fall  of  about  6  feet.  1(t  Round  wooden  piles  were 
driven  8  feet  apart  enclosing  the  site  of  the  83Xi5-foot 
cofferdam;  6X 1 2-in  inside  waling  pieces  were  bolted  to  them 
above  high  water. 

" Spacing  blocks  4  inches  thick  and  i2Xi2-inch  inside  wales 
were  bolted  to  the  outside  wales,  forming  guides,  between 
which  were  driven  a  single  row  of  Lackawanna  1 2-inch,  40- 
pound  steel  sheet  piles  35  feet  long.  These  were  all  assembled 
together  before  driving ....  and  then  driven  ...  by  one 
McKiernan-Terry  steam-hammer  weighing  5000  pounds  and 
making  about  225  strokes  per  minute.  It  was  handled  by  the 

1  Engineering  Record,  vol.  67,  page  268,  March  8,  1913. 


ART.  70 


STEEL    SHEET-PILE    COFFERDAMS 


217 


boom  of  a  floating  derrick  and  went  round  and  round  the  coffer- 
dam, driving  each  pile  a  foot  or  two  at  a  time  until  the  work  was 
completed.  The  driving  was  very  hard,  many  boulders  being 
encountered,  some  of  which  were  displaced  and  others  broken 
by  the  piles.  When  they  could  be  neither  displaced  nor  broken, 
driving  on  the  piles  that  encountered  them  was  discontinued, 
and  adjacent  piles  were  driven  down  to  subgrade  about  6  inches 
below  the  bottom  of  the  footing. 


Plan 


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Concrete  Base 

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1 


Section  A-A 


FIG.  7oa. — Cofferdam  for  Highway  Bridge  Piers  in  Passaic  River,  at  Bridge  St., 

Newark,  N.  J. 

"As  the  bottom  was  excavated  inside  the  cofferdam,  some 
of  the  boulders  which  obstructed  the  sheet  piles  were  left  in 
position  and  the  sides  of  the  excavation  below  them  were 
closed  as  well  as  possible  with  bags  of  cement.  The  cofferdam 
resisted  a  pressure  head  of  about  28  feet  with  very  little  leakage 
through  the  pile  joints,  which  were  packed  with  oakum.  .  .  . 
The  long  sides  of  the  cofferdam  are  braced  with  12X1 2-inch 
horizontal  transverse  struts  9  feet  7  inches  apart  on  centers, 


2l8  COFFERDAMS  CHAP.  VI 

in  four  tiers  about  6  feet  apart.  At  the  rounded  ends  the  in- 
side waling  pieces  are  made  like  arch  centers  of  12X1 2-inch 
double-scarf  pieces,  with  radial  braces  to  the  middle  of  the 
adjacent  cross- strut."- 

Some  of  the  concrete  piers  for  a  bridge  ocross  the  Illinois 
River  at  Peoria,  111.,  were  founded  on  bedrock  20  feet  below  the 
bottom  of  the  river,  where  the  depth  of  water  was  approximately 
20  feet.  To  build  these  piers,  cofferdams  of  steel  sheet-piling 
on  frames  were  used.  By  means  of  an  orange-peel  bucket  the 
material  of  the  river  bottom  was  first  dredged  down  to  a  layer 
of  slate  and  soapstone,  about  3  feet  thick,  which  overlaid  the 
rock.  The  excavation  was  made  over  a  large  area  so  that  the 
material  overlying  the  slate'  would  stand  at  its  natural  slope 
and  still  leave  an  area  on  the  slate  of  sufficient  size  for  the 
cofferdams,  one  of  which  was  39  by  40  feet  in  plan. 

l"The  steel-piling  forming  the  sides  and  ends  of  the  coffer- 
dam was  braced  across  the  latter  with  five  longitudinal  and 
six  transverse  rows  of  12X1 2-inch  timbers  to  hold  it  in  place 
when  the  water  had  been  drawn  down  in  the  cofferdam.  These 
timbers  were  placed  in  nine  horizontal  layers,  varying  from 
i\  to  5  feet  apart  from  the  bottom  to  the  top  of  the  cofferdam. 
The  horizontal  layers  were  held  apart  by  a  vertical  i2X  1 2-inch 
timber  at  each  intersection  of  the  rows  of  braces.  The  timber 
crib  formed  by  these  braces  and  verticals  was  built  in  the  water 
approximately  over  the  site.  The  horizontal  layer  which 
would  come  at  the  level  of  the  top  of  the  slate  and  soapstone 
in  the  cofferdam  was  first  assembled  as  a  raft  on  which  the 
verticals  were  erected  and  then  the  second  horizontal  layer 
was  placed,  sinking  the  crib  thus  formed  to  the  water-level. 
The  various  horizontal  layers  were  thus  added  in  succession 
and  when  they  had  been  completed  the  crib  was  towed  over  the 
site,  sunk  in  position  and  anchored." 

The  steel-piling,  of  the  Friestedt  form,  was  driven  around 
this  framework  through  the  slate  and  soapstone  to  rock,  after 
which  the  material  which  had  been  previously  dredged  was 
backfilled  around  the  cofferdam  up  to  low  water-level.  After 

1  Engineering  Record,  vol.  55,  page  247,  March  2,  1907. 


ART.  70  STEEL    SHEET-PILE   COFFERDAMS  2IQ 

pumping  out  the  cofferdam  the  layer  of  slate  and  soapstone 
was  removed  and  the  pier  built. 

Among  the  deepest  cofferdams  that  have  ever  been  placed 
are  those  used  in  founding  the  piers  of  the  Tunkhannock  Via- 
duct of  the  Delaware,  Lackawanna  &  Western  Railroad. 
These  were  land  cofferdams '  and  had  a  maximum  depth  of 
nearly  100  feet,  with  a  depth  of  65  feet  below  ground  water- 
level.  In  principle  they  closely  resemble  the  method  used  in 
placing  piers  for  buildings  as  described  in  Art.  124,  and  differ 
from  the  regular  caisson  since  excavation  took  place  simul- 
taneously with  the  driving  of  the  sheet-piling,  and  since  the 
lower  part  of  the  sheet-piling  served  as  a  form  for  the  pier 
footing. 

luThe  cofferdam  for  pier  4  is  typical  of  those  of  piers  3,  5,  6,  7 
and  8  and  was  commenced  by  assembling  on  the  surface  of  the 
ground  a  43X49-foot  rectangle  made  of  12X1 2-inch  horizontal 
timbers  spliced  together  to  form  one  course  of  inner  wales. 
Vertical  posts  were  set  up  on  this  course  and  supported  a  second 
similar  course  about  16  feet  above  it,  and  two  corresponding 
courses  of  exterior  wales  were  erected  outside  of  these  and 
about  6  inches  in  the  clear  from  them." 

Lackawanna  steel  sheet-pile  units  30  feet  long  were  then 
placed  between  the  outer  and  inner  wales  and  driven  by  a 
steam-hammer  going  round  and  round  the  cofferdam  driving 
each  pile  unit  2  or  3  feet  at  a  time.  As  the  piling  was  driven  the 
interior  was  excavated  and  the  cofferdam  braced  with  succes- 
sive tiers  of  12X1 2-inch  longitudinal  and  transverse  struts. 

After  driving  this  set  of  piling  to  its  full  length  an  exterior 
row,  concentric  with  the  inner  row  and  4  feet  8  inches  beyond 
the  same,  was  assembled  and  first  driven  to  a  penetration  of 
about  12  to  15  feet.  The  space  between  the  two  rows  was 
then  excavated  and  at  the  same  time  the  inner  row  was  also 
driven,  the  upper  tiers  of  bracing  of  the  latter  being  transferred 
to  the  bottom  and  new  sets  of  bracing  furnished  to  the  outer 
piling.  In  this  way,  by  driving  both  outer  and  inner  rows  to 
their  required  positions,  the  excavation  was  carried  to  rock. 

1  Engineering  Record,  vol.  67,  page  485,  May  3,  1913. 


220 


COFFERDAMS 


CHAP.  VI 


The  advantage  of  two  rows  of  piling  was  in  the  easier  driving 
thereby  obtained.  The  lower  part  of  the  excavation  was  com- 
pletely filled  with  concrete,  the  steel-piling  serving  as  a  form; 


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the  surface  of  the  piling  was  protected  from  the  concrete  by 

tarred  paper,  thus  permitting  the  piling  to  be  with-drawn  later. 

Fig.  706  illustrates  a  somewhat  similar  type  of  cofferdam  used 


ART.    71    SELF-SUPPORTING   STEEL   SHEET-PILE    COFFERDAMS     221 

in  the  reconstruction  of  the  Union  Pacific  Railroad  bridge  at 
Kansas  City.  The  upper  tier  of  sheet-piling  was  of  wood.  The 
details  of  the  bracing  are  clearly  shown  in  the  illustration. 

Fig.  ;oc  is  a  half-tone  showing  the  details  of  the  bracing  used 
for  the  steel  sheet-pile  cofferdam  at  the  Loomis  St.  tunnel, 
Chicago.  The  cofferdam  was  75  by  53  feet  in  plan  and  the 
maximum  head  of  water  on  it  was  about  53  feet.  The  bracing 
consisted  of  i2Xi2-inch  timbers,  spaced  8  feet  apart  hori- 
zontally and  4  feet  vertically. 

Few  examples  exist  of  the  type  of  cofferdam  consisting  of 
steel  sheet-piling  on  cribs.  The  reason  for  this  lies  in  the  fact 
that  almost  all  the  crib  and  sheet-pile  cofferdams  have  been 
built  in  localities  where  timber  is  abundant  and  for  this  reason 
sheet-piling  of  wood  is  cheaper  than  that  of  steel. 

ART.  71.     SELF-SUPPORTING  STEEL  SHEET-PILE   COFFERDAMS 

There  is  a  type  of  cofferdam  using  steel  sheet-piling  which 
has  almost  no  parallel  in  the  wooden  sheet-pile  cofferdam;  this 
is  the  cofferdam  without  horizontal  guides  or  bracing.  Two 
reasons  may  be  given  for  this  fact:  First,  with  the  positive 
form  of  interlock  which  most  forms  of  steel  sheet-piling  po- 
sess,  sufficient  guidance  is  furnished  by  the  interlock  to  do 
away  with  the  necessity  of  horizontal  guides;  and  second, 
the  higher  strength  lessens  the  amount  of  bracing  necessary. 

The  two  most  notable  examples  of  this  type  of  cofferdam 
are  those  used  for  the  United  States  Government  lock  at  Black 
Rock  Harbor,  Buffalo,  N.  Y.,  and  for  raising  the  United  States 
Battleship  " Maine"  in  Havana  Harbor,  Cuba.  Both  of  these 
structures  rank  high  as  daring  pieces  of  cofferdam  work,  the 
former  on  account  of  its  great  size  and  the  latter  because  of 
its  great  height. 

The  Black  Rock  cofferdam  was  built  to  permit  the  construc- 
tion of  a  ship  lock,  and  was  rectangular  in  plan,  260  by  947 
feet  over  all  as  shown  in  Fig.  710.  The  depth  of  water  at  the 
site  varied  from  2  to  15  feet,  averaging  about  8  feet,  while  the  solid 
rock  on  which  the  lock  was  built  was  about  40  feet  below  mean 
water-level.  As  shown  in  Fig.  716  the  sides  of  the  cofferdam 


222 


COFFERDAMS 


CHAP.  VI 


were  made  of  two  walls  of  steel  sheet-piling,  the  space  between 
the  two  walls  being  divided  into  pockets  30  feet  square  by 
transverse  walls  of  the  same  piling  as  that  used  for  the  main 
walls,  which  served  to  connect  the  latter.  A  horizontal  15- 
inch,  40-pound  channel  was  bolted  to  the  tops  of  the  piles  of  the 
inner  wall  and  a  similar  channel  was  bolted  at  an  inclination 
across  the  transverse  walls  as  shown  in  Fig.  yic. 

The  piling  was  driven  to  rock  and  at  first  wooden  guide 
piles  and  wales  were  used  to  maintain  the  alignment  of  the  steel 
sheeting,  but  eventually  these  guides  were  dispensed  with,  the 

3  Q UA  W                 ISLAND 
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ff-ED:'  M  1 1  i  M  1 1  M»I  1 1  i  isoi  n  i  kimnifc 
^sK^^Sr~-5S«S^iri^^^^^s^i 


FIG.  710.— Plan  of  Black  Rock  Cofferdam. 

only  ones  used  being  ioX3o-foot  floating  forms  having  one 
edge  in  the  plane  of  the  sheeting.  The  fine  alignment  at- 
tained by  this  simple  method  may  be  seen  in  Fig.  jib.  After 
driving  the  piling  the  pockets  were  filled  with  clay  and  to 
further  strengthen  the  structure,  as  the  inside  was  excavated, 
a  bank  of  earth  25  feet  high  was  maintained  on  the  inside  as 
shown  in  Fig.  jic.  But  in  spite  of  this  bank  of  earth  the 
material  in  the  pockets  caused  the  inside  wall  to  bulge  badly 
between  the  cross  walls  in  both  a  horizontal  and  vertical 
direction. 

It  is  instructive  to  observe  the  plans  of  different  pockets  of 
the  cofferdam,  and  the  curvature  of  vertical  sections  after 
the  steel  sheet-piling  adjusted  itself  to  the  pressure  of  the  clay 
filling  by  developing  tension  in  the  interlock.  Fig.  71  d  gives  the 


ART.  71     SELF-SUPPORTING    STEEL   SHEET-PILE   COFFERDAMS    223 

results  of  a  careful  survey  of  pocket  No.  35  in  which  the  maxi- 
mum bulging  of  sides  occurred.  It  should  be  noted  how  short  a 
distance  the  bulging  extended  below  the  sand  and  gravel  bank 
which  was  allowed  to  remain  inside  of  the  cofferdam.  The 
diagram  also  shows  vertical  sections  at  the  middle  of  pock- 
ets Nos.  30,  52,  and  75,  the  relative  location  of  the  pockets 
being  indicated  in  Fig.  710.  See  also  the  half-tone  view, 
Fig.  7  ic. 


Section  A-B. 
FIG.   7 id. — Diagram  Showing  Deformation  of  Steel  Sheet  Piling. 

In  all  6589  tons  of  steel  sheet-piling  were  used  in  this  coffer- 
dam, there  being  6870  linear  feet  of  piling  wall  from  45  to  50 
feet  high,  which  makes  this  the  largest  piece  of  cofferdam  sheet- 
piling  work  on  record  to  1914.  The  price  paid  the  contractor  for 
building  the  cofferdam,  which  included  furnishing  all  material, 
pumping  out,  and  maintaining  the  same,  was  $408  830.  The 
type  of  piling  used  was  that  known  as  the  Lackawanna,  and 
which  had  a  web  thickness  of  J  inch  and  weighed  40  pounds 
per  linear  foot. 


224  COFFERDAMS  CHAP.  VI 

The  cofferdam  for  raising  the  " Maine"  represents  a  special 
type  of  steel  cofferdam,  very  large  and  strong.  l  "The  problem 
was  to  surround  the  wreck  of  the  vessel,  lying  in  about  29  to  37 
feet  of  water,  with  a  cofferdam,  which  when  unwatered  would 
be  tight  enough  to  prevent  leakage,  strong  enough  to  resist 
outside  water  and  mud  pressures,  and  a  protection  that  would 
assure  safety  during  the  work.  The  cofferdam  should  be  self- 
sustaining,  if  possible.  Bracing  by  struts  across  its  interior  to 
resist  the  water  and  mud  pressures  might  be  difficult  to  install 
and  would  interfere  with  the  operation  of  removal.  The  bor- 
ings indicated  bad  conditions  for  foundations.  The  building 
of  a  cofferdam  without  internal  bracing,  which  would  withstand 
pressures  from  a  head  of  37  feet  of  water  and  practically  21  to 
23  feet  of  mud,  was  an  unprecedented  task. 

"The  cofferdam  should  be  not  only  self-sustaining  and  safe 
against  the  pressures  to  which  it  was  to  be  exposed,  but  it  should 
also  be  capable  of  complete  removal  after  it  had  served  its 
purpose.  It  should  be  able  to  support  more  or  less  superim- 
posed loads,  for  working  platforms  had  to  be  built  upon  it.  The 
work  of  unwatering  the  area  enclosed  had  to  be  carried  on  from 
the  top  of  the  cofferdam;  and  afterward,  men  and  materials  had 
to  be  transferred  from  there  to  the  interior,  for  work  upon  the 
wreck.  .  .  .  The  cofferdam  decided  upon  consisted  of  20 
equal  cylinders,  50  feet  in  diameter,  and  composed  of  steel- 
piling  75  feet  long.  .  .  . "  A  plan  is  shown  in  Fig.  710. 

"The  length  of  the  major  axis  of  the  cofferdam  was  prac- 
tically 399  feet,  and  of  the  minor  axis  219  feet,  leaving  a 
2o-foot  clearance  at  the  submerged  bow  of  the  ship  and  a  i4-foot 
clearance  at  the  stern,  with  45  feet  at  the  side  cylinders.  Such 
clearance  was  necessary  to  avoid  portions  of  the  wreck  which 
had  been  blown  beyond  the  position  occupied  by  the  hull. 

"The  units  of  the  cofferdam  were  made  cylindrical  for  the 
reason  that  the  extremely  high  pressures, which  would  be  exerted 
by  the  mud  rilling,  would  act  radially  and  uniformly  on  each 
pile,  straining  each  joint  to  the  same  amount  at  equal  depths, 

1  Bulletin  No.  102,  Lackawanna  Steel  Co.,  Buffalo,  N.Y. 


ART.  71    SELF-SUPPORTING    STEEL   SHEET-PILE   COFFERDAMS     225 


FIG.   jie. — Plan  of  Cofferdam  for  Raising  the  "Maine." 


FIG.   7  if. — Connection  of  Cofferdam  Cylinders. 


L 


FIG.   7ig. — Filling  Clay  into  Cylinder  A .     Part  of  B  in  Foreground. 


226  COFFERDAMS  CHAP.  VI 

and  in  the  entire  cofferdam  cylinders  would  deform  least  from 
play  in  the  piling  interlocks." 

The  cylinders  were  driven  tangent  to  one  another  and  to  in- 
sure their  stability  and  prevent  leakage  of  water  through  them 
when  the  cofferdam  was  pumped  out  they  were  filled  to  the  top 
with  clayey  material  that  was  dredged  from  the  bottom  of  the 
harbor.  A  curved  diaphragm  of  steel-piling,  as  shown  in  Fig. 
7  if,  was  driven  to  connect  adjacent  cylinders,  and  the  space 
between  this  arc  and  the  outer  surfaces  of  the  large  cylinders 
was  likewise  filled  with  dredged  material. 

The  piling  used  was  the  Lacka wanna  section,  weighing  35 
pounds  per  linear  foot,  and  had  a  web  \  inch  thick.  The  piles 
were  driven  so  that  their  tops  were  2  or  3  feet  above  normal 
water-level  (Fig.  yig)  and  the  75-foot  length  of  piling,  which 
penetrated  the  harbor  bottom  to  a  distance  of  approximately  35 
feet,  was  made  of  two  lengths  spliced  together  with  channels. 

ART.  72.     CRIB  COFFERDAMS 

Where  the  cofferdam  is  to  rest  on  bedrock  which  is  ap- 
proximately smooth  and  level,  a  crib  cofferdam,  formed  with  one 
or  two  walls  of  squared  horizontal  timbers  laid  closely,  may  be 
used  in  place  of  the  sheet-pile  cofferdam.  Where  the  single- 
wall  type  is  used  it  is  ordinarily  made  an  integral  and  permanent 
part  of  the  pier,  and  as  such  is  not  a  cofferdam,  but  a  caisson. 
For  a  description  of  this  type  see  Art.  83. 

In  his  book  on  Sub-aqueous  Foundations,  FOWLER  describes  a 
double- wall  crib  cofferdam  used  by  the  C.  B.  &  Q.  R.  R., 
which  was  made  from  2X8-inch  and  2Xio-inch  fence  boards 
laid  flat.  The  two  walls  were  thoroughly  tied  together  and  the 
space  between  filled  with  puddle. 

Fig.  72  a  shows  a  polygonal  cofferdam  of  the  crib  type  which 
was  used  for  the  center  pier  of  the  Arthur  Kill  Bridge.  At  the 
site  of  the  cofferdam  the  depth  of  water  at  high  tide  was  about 
28  feet,  with  about  4  feet  of  mud  and  clay  overlying  bedrock. 
This  mud  and  clay  was  dredged  out  previously  to  placing  the 
cofferdam.  The  latter  had  twelve  sides  with  walls  4  feet  apart 
in  the  clear,  and  in  this  space  puddle  was  dumped.  All  courses 


ART.  72 


CRIB    COFFERDAMS 


227 


of  timber  were  thoroughly  drift-bolted  together  and  all  joints 
caulked  with  cotton  wicking.  No  internal  bracing  was  used. 
Before  pumping  out  the  water  a  4-foot  layer  of  concrete  was 
deposited  all  over  the  bottom  and  allowed  to  harden  for  a  week. 
The  cofferdam  for  the  new  inlet  tower  of  the  St.  Louis  Water- 
works was  of  the  double-wall  crib  type,  38  by  76  feet  in  plan 
and  22  feet  high.  The  walls  were  composed  of  horizontal 
12 X i2-inch  material  and  were  3  feet  apart  in  the  clear.  The 
joints  between  all  courses  were  carefully  caulked.  The 
cofferdam  was  braced  transversely  by  three  vertical  rows  of 


M.H.W. 


nearfy  Level. 
Section  of  Dam. 


Plan  of  Dam. 
FIG.   720. — Cofferdam  for  Pivot  Pier  of  Arthur  Kill  Bridge. 

horizontal  12X1 2-inch  timbers  spaced  4  feet  apart  vertically, 
and  extending  from  outside  wall  to  outside  wall,  thus  tying  the 
walls  together  as  well  as  bracing  the  cofferdam.  The  ends  were 
braced  by  similar  horizontal  i2Xi2-inch  diagonal  timbers, 
running  at  an  angle  of  about  45  degrees  from  the  center  of 
the  ends  to  the  sides. 

The  river  bottom  was  bedrock  and  the  depth  of  water  about 
15  feet,  the  current  having  a  velocity  of  from  6  to  8  miles  an 
hour.  The  cofferdam  was  held  in  place  by  three  triangular 


228  COFFERDAMS  CHAP.  VI 

cribs  filled  with  rocks  and  sunk  upstream  from  the  cofferdam 
and  tied  to  the  latter  by  cables.  The  puddle  chamber  was 
partly  filled  with  concrete  in  sacks  and  puddle  placed  on  top. 
Sacks  of  clay  were  also  banked  around  the  outside. 

Cofferdams  are  widely  used  as  temporary  adjuncts  to  open 
and  pneumatic  caissons,  but  as  the  details  differ  widely  from 
the  types  described  in  this  chapter  and  resemble  closely  the 
caissons  themselves  they  will  be  described  in  the  chapters 
dealing  with  such  caissons. 

ART.  73.     MOVABLE  COFFERDAMS 

Unless  it  forms  an  obstruction  to  navigation  only  that  part 
of  the  cofferdam  above  low  water  is  sometimes  removed. 
This  is  because  the  salvage  value  of  the  material  is  less 
than  the  cost  of  getting  it  out,  except  where  steel  sheet-pil- 
ing is  used. 

Where  the  same  size  and  style  of  cofferdam  is  to  be  used 
for  a  number  of  piers  it  will  often  prove  advantageous  to  so 
construct  a  cofferdam  that  it  can  be  used  over  and  over  again. 
In  one  type,  that  of  the  cofferdam  on  grillage,  it  is  so  easy  to 
make  its  sides  removable  that  it  is  universally  done,  even 
though  they  may  not  be  used  a  second  time. 

A  movable  cofferdam  consisting  of  sheet-piling  supported 
by  a  crib  was  used  in  constructing  the  piers  of  the  Falls-of- 
Schuylkill  Bridge,  of  the  Philadelphia  &  Reading  Railroad. 
When  in  position  the  cofferdam  was  62  feet  long,  36  feet  wide 
and  16  feet  high.  The  cribs  were  10  feet  thick,  making  the 
inside  dimensions  42X16  feet.  The  cofferdam  was  divided 
vertically  through  each  short  side  into  two  parts  of  equal  size 
and  these  were  floated  separately  to  the  site,  joined  together 
and  sunk.  Each  section  had  water-tight  compartments  to  assist 
in  floating  and  these  were  filled  with  water  and  stone,  while 
other  non-water-tight  compartments  were  filled  with  stone, 
when  it  was  desired  to  sink  the  sections.  On  reaching  the 
rock  bottom  sheet-piling  of  jointed  planks,  3  or  4  inches  thick, 
was  placed  on  the  outside  and  spiked  there.  Puddle  was  then 
placed  around  the  outside,  after  which  the  cofferdam  was 


ART.  73 


MOVABLE    COFFERDAMS 


229 


pumped  out.     Two  sets  of  horizontal  bracing  connecting  the 
long  sides  were  placed  as  the  water  was  removed. 

In  placing  cylinder  piers  for  the  Queen's  Bridge,  Melbourne, 
Australia,  square  movable  cofferdams  of  the  sheet-pile-on-frame 
type  were  used.  One  side  opened  outward  as  a  door,  thus  per- 
mitting the  cofferdam  to  be  removed  on  completion  of  a  pier. 
laThe  dam  was  built  on  shore  complete,  and  launched  ready 
for  immediate  use  on  the  site  of  a  cylinder.  The  sheet-piling 
was  vertical  and  consisted  of  i2X4-inch  rough-sawn  Oregon 
planks,  supported  by  horizontal  frames  of  12X1 2-inch  Oregon 
timber,  spaced  close  together  near  the  bottom  of  the  river,  to 


3"x8" 


6x8" 


25' 0" 


6"xlO" 


6"x8' 


Longitudinal  Section. 


Cross  Section. 


BothSidet 

?  Smoothed 

andEdges 

Beveled 


PI  ah.  Corner  Details. 

FIG.  730. — Cofferdam  Used  on  Key  West  Extension  of  Florida  East  Coast  Railway. 

carry  the  greater  pressure  of  water.  Up  the  four  corners  of  the 
dam  were  i2Xi2-inch  Oregon  timbers,^into  which  the  frames 
were  checked  and  by  which  they  were  kept  to  their  proper 
spacing,  and  which  formed  supports  for  the  door.  Outside 
the  sheet-piling,  at  the  top  and  bottom  frames  there  were 
outside  wales,  12  by  6  inches  (keeping  the  sheet-piling  in  place), 
bolted  to  the  frames  inside  by  i-inch  bolts,  two  to  each  waie, 
passing  between  two  sheet  piles."  The  sheet-piling  was  flush 

1  Engineering  News,  vol.  33,  page  230,  April  4,  1895. 


230 


COFFERDAMS 


CHAP.  VI 


with  the  bottom  of  the  frame  and  extended  a  few  feet  above 
the  top. 

At  the  site  of  the  piers  there  was  about  3  feet  of  soft  silt 
covering  the  rock.  This  silt  was  covered  with  puddle  before 
placing  the  cofferdam.  After  sinking  it  by  weighting,  the  sheet- 
piling  was  driven  through  the  puddle  and  silt.  On  pumping 
out  the  cofferdam  much  of  the  silt  ran  into  the  interior  and  the 
clay  took  its  place,  thus  sealing  the  structure.  To  remove  the 
cofferdam  the  sheet-piling  was  first  drawn  up,  the  loading 
taken  off,  the  door  opened,  and  the  cofferdam  floated  out.  At 

\ffemove  fhis  Top  Cross- Brcrce  erncf 

Base  of  Rail  El.  +11.05  -,.\brace  Concrete  Form  from  Side  +IW5 
\  ]  Posts  as  indicated  in  dotted  Lines^~K'fiT]£ 
i  \before  Coping-Course  is  put  on 

,!<-"-• /£•£-""— >]'   &• 

I    eTI          !  '      °o. 


Part  Sectional    Side    Elevation.  Sectional    Side    Elevation. 

FIG.  73&. — Cofferdam  for  Rest  Pier  of  Chicago  and  Northwestern  Railway  Lift 

Bridge  at  Kinzie  Street,  Chicago. 

first  tarpaulin  was  placed  around  the  outside  of  the  cofferdam 
but  it  was  later  found  that  this  was  unnecessary  since  the 
sheet-piling  was  water-tight  without  it. 

Fig.  730  illustrates  the  form  of  a  movable  cofferdam  used  in 
constructing  the  piers  of  the  Key  West  Extension  of  the  Florida 
East  Coast  Railway,  where  the  depth  of  water  did  not  exceed 
8  feet.  The  two  sides  and  the  two  ends  formed  independent 
portable  sections  which  were  connected  together  by  means  of 
ij-inch  vertical  rods  running  down  through  the  overlapping 
rangers  at  the  corners  of  the  cofferdam. 


ART.  73 


MOVABLE   COFFERDAMS 


23I 


Detail  at  A 


4x6 'about  6'0'cJoc. 


At  the  site  of  the  piers  sand  overlaid  the  coral  rock.  Piles, 
for  the  foundation  of  the  pier,  were  first  driven  until  the  tops 
were  2  feet  below  low  water,  after  which  the  cofferdam  was 
assembled  on  a  barge,  lifted  from  the  same  and  set  in  place. 
The  sand  was  then  pumped  out  by  a  centrifugal  pump,  after 
which  a  2-foot  seal  of  concrete  was  placed  over  the  whole 
bottom.  After  allowing  this  concrete  to  harden  for  seven 
days,  the  cofferdam  was  pumped  out,  forms  placed  and  the 
pier  built.  On  completion  of  the 
pier  the  rods  were  withdrawn,  which 
allowed  the  sections  to  float  free. 

MOVABLE  COFFERDAMS  ON  GRIL- 
LAGE.— On  account  of  its  conven- 
ience and  ease  of  manipulation  a 
movable  cofferdam  is  almost  uni- 
versally employed  where  a  timber 
grillage  foundation  on  piles  is  used 
for  the  pier.  The  grillage  and  the 
cofferdam  form  an  open  box  con- 
structed on  shore  or  on  a  barge  or 
raft,  launched,  floated  to  the  site, 
and  sunk  on  the  pile  foundation  by 
building  the  pier  in  the  box.  This 
type  differs  from  the  box  caisson, 
described  in  Art.  80,  since  the  sides 
of  the  former  are  not  a  permanent 
part  of  the  pier.  After  the  pier  is  built  to  above  high-water 
level  the  cofferdam  is  removed,  the  sides  being  so  fastened  to 
the  grillage  that  this  can  easily  be  done. 

Fig.  736  shows  the  details  of  the  movable  cofferdam  used  for 
the  i2X4il*-foot  pier  of  the  Kinzie  St.  drawbridge,  in  Chicago. 
This  cofferdam  was  connected  to  the  grillage  by  28  vertical 
i-inch  rods,  2  if  feet  long.  To  sink  the  structure,  concrete 
forming  the  pier  was  placed  in  the  same,  the  cofferdam  itself 
serving  as  a  form  for  the  concrete  up  to  an  elevation  shown  in 
the  drawing,  and  above  this  regular  forms  were  used.  On  com- 


Sect  ion  of  Cpisson 


FIG.   73<r.  —  Cofferdam  with 
Removable  Sides. 


232  COFFERDAMS  CHAP.  VI 

pletion  of  the  pier  the  rods  were  removed,  which  permitted  the 
removal  of  the  cofferdam  from  the  grillage. 

A  very  simple  cofferdam  on  grillage  was  used  in  building  the 
foundation  piers  of  the  Bellevue  Hospital  Boiler  House,  a 
section  of  which  may  be  seen  in  Fig.  73^.  The  largest  was 
approximately  14X52  feet  in  plan  and  12^  feet  high.  The 
most  interesting  feature  is  the  very  thin  grillage  used,  it 
being  composed  of  two  crossed  courses  of  2-inch  tongue-and- 
grooved  planks.  It  was  desired  to  use  a  thickness  which  would 
give  enough  strength  for  launching  and  sinking  stresses,  and 
yet  be  sufficiently  flexible  so  that  a  uniform  bearing  over  the 
slightly  irregular  pile  tops  would  be  secured. 

ART.  74.     MISCELLANEOUS  TYPES 

The  foregoing  articles  have  dealt  with  what  may  be  called 
standard  types  of  cofferdams,  but  there  have  been  many  coffer- 
dams constructed  which  are  either  a  combination  of  any  two 
standard  types  or  which  differ  fundamentally  from  those  which 
have  been  described.  For  instance  in  the  cofferdam  for  the 
Dearborn  St.  bridge,  Chicago,  a  double-wall  sheet-pile  coffer- 
dam was  used,  the  outer  wall  being  composed  of  Wakefield 
sheet-piling  and  the  inner  wall  of  Friestedt  steel  sheet-piling, 
thus  giving  a  composite  wood  and  steel  sheet-pile  cofferdam. 

Fig.  740  shows  a  form  of  cofferdam  known  as  the  A-frame 
type  which  is  used  on  bedrock.  This  particular  one  was  used 
on  the  New  York  Barge  Canal  and  consisted  of  a  series  of  bents, 
spaced  6  feet  center  to  center.  On  these  bents  rested  purlins, 
which  in  turn  supported  the  sheathing  of  jointed  and  caulked 
3-inch  planking.  As  shown  in  the  illustration,  the  structure 
was  braced  against  sliding  by  having  certain  of  the  struts 
bear  against  concrete  footings  on  the  rock.  This  form  of  bear- 
ing can  be  made  only  when  the  rock  is  exposed  at  times.  The 
maximum  head  of  water  supported  was  18  feet. 

Another  cofferdam  of  the  same  type  was  used  for  some  canal 
work  at  Keokuk,  Iowa.  Here  it  was  necessary  to  construct 
the  cofferdam  without  drawing  off  the  water  in  the  canal, 


ART.  74 


MISCELLANEOUS   TYPES 


233 


and  hence  it  was  built  away  from  the  site,  brought  to  place, 
and  sunk  by  weighting  with  iron  rails.  Water- tightness  was 
promoted  by  covering  the  sheathing  with  canvas. 

In  constructing  concrete  wharves  at  Fort  Mason,  San  Fran- 
cisco, steel-cylinder  cofferdams,  7  feet  7  inches  in  diameter  and 
50  feet  long,  were  used  in  which  to  construct  reinforced-con- 
crete  piers.  These  cylinders,  weighing  17  tons  each,  were 
driven  by  a  pile-driver  through  the  bottom  and  into  hard-pan, 
after  which  the  water  was  bailed  out,  the  mud  removed,  wooden 


SheerP/l 
FIG.   74a. — A-Frame  Cofferdam  Used  on  New  York  State  Barge  Canal. 

forms  placed  and  the  4-foot  reinforced-concrete  piers  with  en- 
larged bases,  6^  feet  in  diameter,  cast.  After  the  concrete  had 
set  the  cylinders  were  pulled  by  the  pile-driver,  the  required 
pull  being  about  50  tons. 

In  vol.  26  of  Revue  Technique,  the  proposed  design  for  a 
cofferdam  of  ice  to  close  the  entrance  to  the  outer  basin  at  the 
Port  of  La  Rochelle  is  described.  The  freezing  was  to  be  done 
with  refrigerating  machines,  sheathings  of  non-conducting 
material  being  placed  between  the  water  to  be  frozen  and  that 


234  COFFERDAMS  CHAP.  VI 

to  be  left  unfrozen.     It  was  estimated  that  such  a  cofferdam 
would  cost  less  than  any  ordinary  form. 

Another  proposed  type  described  in  the  same  article  was  of 
reinforced  concrete.  It  was  designed  with  inclined  sides,  the 
width  of  the  base  being  19.7  feet,  the  width  of  the  top  4.9  feet, 
and  the  thickness  of  the  walls  about  10  inches.  The  walls  were 
to  be  well  braced  by  struts.  The  structure  was  to  be  built 
away  from  the  site,  floated  to  place  and  sunk  by  filling  with 
clay.  It  was  estimated  that  it  would  have  sufficient  stability 
to  withstand  a  head  of  24.6  feet  of  water. 

ART.  75.     PUDDLE  AND  LEAKAGE 

It  is  seldom  attempted  to  construct  a  water-tight  cofferdam, 
for  the  cost  of  such  is  usually  prohibitive.  The  greatest 
trouble  from  leakage  occurs  in  the  case  of  cofferdams  which 
rest  on  rock,  for  here  it  is  almost  impossible  to  prevent  the 
water  from  running  in  between  the  bottom  of  the  cofferdam  and 
the  rock.  But  if  the  structure  rests  on  clay  and  the  sheet- 
piling  is  driven  well  down  there  will  be  but  a  slight  amount  of 
leakage  at  this  point.  Where  the  leakage  occurs  through  seams 
in  the  rock  it  may  be  stopped  by  filling  the  seams  with  grout 
pumped  in  through  pipes  about  4  inches  in  diameter.  Another 
method  is  to  dump  clay,  sand,  ashes,  etc.,  all  around  the  coffer- 
dam with  a  view  of  shutting  off  the  water-supply  of  the  crevices. 
When  the  leakage  is  due  to  irregularities  in  the  rock  surface, 
concrete  in  bags  may  be  placed  on  the  bottom,  or  water-logged 
oat  straw  may  be  sunk  by  mixing  with  ashes  or  covered  with 
a  wire  net  loaded  with  sand  and  clay,  after  which  the  rest 
of  the  puddle  filling  may  be  placed.  Another  method  of  pre- 
venting leakage  on  a  rock  bottom  is  to  use  canvas  as  noted  in 
previous  articles. 

Leaks  often  develop  in  double-wall  cofferdams  by  the  filling 
between  the  walls  not  compacting  well,  or  settling  after  being 
placed  and  leaving  openings  beneath  cross  braces.  To  com- 
pact this  filling  piles  are  sometimes  driven  into  it  or  stock  ram- 
ming may  be  resorted  to.  The  latter  consists  of  forcing 
clay  cylinders  through  pipes  into  the  filling. 


ART.  76  DESIGN  OF   COFFERDAMS  235 

The  ideal  puddle  for  a  cofferdam  is  a  mixture  of  clay  and  sand 
or  clay  and  gravel.  The  sand  or  clay  alone  is  almost  worth- 
less, the  sand  because  of  its  permeability  and  the  clay  on  account 
of  its  tendency  to  allow  a  leak  once  started  to  enlarge  rapidly 
through  the  clay  arching  over  the  leak,  instead  of  falling  into  and 
stopping  the  same.  The  ideal  mixture  obtains  when  there  is 
just  enough  coarse  material  in  it  to  reduce  the  cohesion  of  the 
mass  sufficiently  to  prevent  this  arching  action. 

ART.  76.     DESIGN  OF  COFFERDAMS 

Like  most  structures  used  in  foundations,  a  purely  theoretical 
design  of  cofferdams  leads  to  unsatisfactory  results.  For  some 
types  it  is  a  simple  matter  to  design  the  structure  to  resist  the 
hydrostatic  pressure,  but  to  design  it  properly  to  resist  safely  the 
pressure  of  the  earth  filling,  or  of  freshets,  ice,  or  floating  logs, 
requires  much  experience. 

Earth  cofferdams  usually  fail  by  the  water  seeping  through 
and  enlarging  a  channel  until  a  washout  takes  place.  For  this 
reason  such  cofferdams  should  be  carefully  watched  to  detect 
small  leaks  that  they  may  be  checked  quickly  after  starting. 
In  general,  if  the  cofferdam  is  madeo  f  a  good  mixture  of  clay  and 
sand,  has  a  width  of  at  least  3  feet  at  the  top,  which  is  well  above 
high  water,  and  has  sides  inclined  at  the  natural  slope  of  the 
material,  the  cofferdam  will  be  safe. 

In  the  single-wall  sheet-pile  cofferdam  with  guide  piles,  if  the 
wales  are  at  the  top  and  bottom,  the  sheet  piles  may  be  assumed 
to  act  as  simple  beams,  with  a  load  per  vertical  foot  varying 
uniformly  from  zero  at  the  water  surface  to  a  value  of  wd 
pounds  per  square  foot  at  the  surface  of  the  earth,  where  w  is 
the  weight  in  pounds  of  a  cubic  foot  of  water  and  d  the  depth  of 
the  water  in  feet.  For  a  discussion  of  the  design  of  sheet-piling 
see  Art.  63.  The  wales  take  the  reactions  of  the  sheet-piling 
and  transfer  them  as  supported,  partially  continuous,  or  con- 
tinuous beams,  to  the  guide  piles.  Conservative  engineers 
usually  design  the  wales  as  simple  or  supported  beams.  If  no 
bracing  is  used  the  guide  piles  should  be  designed  as  cantilever 
beams  with  loads  coming  from  the  waling  pieces.  The  maxi- 


236  COFFERDAMS  CHAP.  VI 

mum  moment  will  occur  at  or  below  the  mud  line.  If  firmly 
braced  at  the  top  by  struts  extending  across  the  cofferdam,  it 
will  be  best  to  design  the  guide  piles-as  simple  beams. 

Each  wall  of  the  double-wall  sheet-pile  cofferdam  with  guide 
piles  may  be  designed  somewhat  in  accordance  with  the  above 
outline.  The  outer  wall  will  be  subjected  to  water  pressure 
from  the  outside  and  earth  pressure  from  the  inside.  Expe- 
rience shows  that  usually  the  pressure  from  the  puddle  will,  for 
equal  heads,  be  larger  than  the  pressure  from  the  water.  This 
will  cause  a  stress  in  the  tie  rods  connecting  the  two  walls. 
The  inner  wall  must  be  designed  to  resist  the  forces  due  to  the 
puddle  filling. 

In  the  design  of  a  cofferdam  composed  of  sheet-piling  on 
frames  and  the  corresponding  bracing,  the  hydrostatic  pressure 
is  the  only  force  to  be  considered.  The  sheet-piling  acts  as  a 
simple  beam  between  horizontal  rangers,  and  the  latter  act  as 
beams  between  bracing  struts. 

The  sheet-pile-on-crib  cofferdam  must  be  designed  so  that 
the  cribs  will  not  overturn  or  slide.  To  be  safe  against  sliding 
the  weight  of  the  cribs  and  filling  per  linear  foot  of  length, 
multiplied  by  the  coefficient  of  friction  between  the  crib  and 
rock,  must  be  greater  than  wd2/2,  where  the  terms  have  the  same 
meaning  as  those  previously  given.  To  be  safe  against  over- 
turning the  weight  per  linear  foot  of  length,  including  filling, 
multiplied  by  one-half  the  width,  must  be  greater  thanwd3/6. 

Before  attempting  to  design  a  cofferdam  the  literature  on  the 
subject  should  be  carefully  read,  for  as  stated  in  the  first  part  of 
the  article  no  purely  theoretical  design  will  result  in  a  thoroughly 
satisfactory  structure.  In  the  preceding  articles,  standard 
types  and  standard  methods  of  construction  are  described  and 
a  careful  reading  of  this  material  will  help  the  inexperienced 
engineer.  For  more  detailed  information  the  reader  is  referred 
to  the  carefully  selected  list  of  references  in  Chap.  XIX. 

ART.  77.     COST  OF  COFFERDAMS 

Little  value  attends  the  mere  statement  of  cost  of  engineering 
works  unless  all  the  conditions  are  fully  described  (see  Engineer- 


ART.  77  COST   OF   COFFERDAMS  237 

ing  NeWs,  vol.  70,  page  1305,  Dec.  25,  1913).  For  this  reason 
only  a  few  figures  will  be  given  here.  In  Art.  71  the  cost  to 
the  United  States  of  the  steel  sheet-pile  cofferdam  at  Black 
Rock  Harbor  is  given. 

THOMAS  P.  ROBERTS  writes1  that  for  large  cofferdams  con- 
structed in  the  rivers  near  Pittsburgh,  Pa.,  the  cost  per  linear 
foot  of  cofferdam  will  vary  from  $8  to  $10.  These  cofferdams 
are  of  the  double- wall  type,  from  10  to  12  feet  wide  and  from  14 
to  1 6  feet  high.  Two-inch  hemlock  sheet-piling  is  used. 

In  constructing  some  piers  for  a  bridge  over  Paint  Creek, 
near  Chillicothe,  Ohio,  where  the  water  was  from  3  to  6  feet 
deep,  a  single-wall  steel  sheet-pile  cofferdam,  16  by  62  feet  in 
plan,  was  used.  The  piling  was  16  feet  long  and  was  driven 
into  the  gravel  bottom  until  the  top  of  the  same  was  2  feet 
above  water-level.  The  bracing  consisted  of  two  horizontal 
wales  at  the  top,  running  longitudinally  and  cross-braced  with 
struts.  The  first  cost  of  the  sheet-piling  was  about  $182 2,  and 
as  the  same  piling  was  used  for  five  cofferdams,  the  cost  per 
cofferdam  was  about  $364.  The  cost  of  placing  two  of  the  coffer- 
dams averaged  $94,  while  the  cost  of  removing  the  piling  per 
cofferdam  was  $47,  thus  making  the  total  cost  of  each  cofferdam 
about  $505. 

In  1886,  near  the  same  site,  some  cofferdams  of  the  double- 
wall  type  were  built  with  wooden  sheet-piling  on  guide  piles. 
For  the  river  piers  the  cofferdams  were  22  by  45  feet  inside  and 
35  by  58  feet  outside.  The  guide  piles  were  about  8  feet  apart. 
The  wales  were  3  inches  thick  and  the  sheet-piling  was  made  of 
2-inch  planking.  The  bid  for  the  construction  of  these  two 
cofferdams  averaged  about  $569,  the  unit  prices  being  as  fol- 
lows: timber  $24  per  1000  feet  B.  M.,  piles  30  cents  per  linear 
foot,  iron  bolts  5  cents  per  pound,  and  earth  filling  in  cofferdam 
30  cents  per  cubic  yard.  At  the  time  the  steel  cofferdams  were 
built  (about  1905)  the  cost  of  the  double-wall  cofferdams  would 
probably  have  been  between  30  and  40  percent  greater  than  in 
1886.  These  figures  show  the  considerable  economy  of  coffer- 
dams in  which  steel  instead  of  timber  sheet-piling  is  employed. 

1  Engineering  News,  vol.  54,  page  138,  Aug.  10,  1905. 


238  COFFERDAMS  CHAP.  VI 

ART.  78.     CHOICE  OF  TYPE 

The  best  type  to  use  in  any  particular  case  is  that  one  which 
fulfills  all  the  required  functions  at  a  minimum  cost.  Where  the 
depth  of  water  is  not  great,  and  the  danger  of  overflow  and  wash- 
ing away  does  not  occur,  the  simple  earth  cofferdam  will  prove 
the  cheapest  and  most  satisfactory,  especially  if  the  site  of  the 
permanent  foundation  must  be  excavated  to  some  depth;  for 
in  this  case  the  excavated  material  may  be  used  to  form  the 
cofferdam.  Where  the  depth,  of  water  is  considerable  the 
width  of  the  cofferdam  becomes  so  great  that  this  type  is  not 
economical. 

Where  the  bottom  can  be  penetrated  with  piles  the  sheet-pile 
cofferdam  with  guide  piles  is  a  very  satisfactory  type.  For 
high  heads  the  double-wall  cofferdam  will  be  used.  This  form 
approximates  somewhat  the  earth  cofferdam,  but  possesses  the 
advantage  over  it  that  less  earth  is  required,  and  it  is  also  a 
stronger  structure  and  more  nearly  water-tight.  The  single- 
wall  type  obstructs  the  water-way  less  than  does  that  with 
double  walls,  but  it  has  less  strength.  If  bracing  can  be  used 
on  the  inside  the  latter  can  usually  be  made  sufficiently  strong 
to  withstand  any  forces  that  are  likely  to  come  upon  it. 

Where  the  bottom  is  composed  of  rock  a  sheet-pile  cofferdam 
on  a  frame  or  cribs  will  be  used.  Frames  are  used  where  the 
cofferdam  can  be  braced  across  by  struts,  but  where  the  struc- 
ture is  too  large  for  such  bracing,  cribs  are  necessary.  The  crib 
cofferdam  may  be  said  to  have  gone  out  of  use,  the  open  caisson 
having  taken  its  place.  Where  the  cofferdam  is  not  large  and 
the  same  size  is  to  be  used  a  number  of  times  some  form  of 
movable  structure  should  be  adopted. 

As  to  whether  wooden  or  steel-piling  should  be  used  in  any 
particular  case  becomes  simply  a  question  of  the  relative  cost 
of  the  two  types.  In  general,  the  steel-piling  will  be  used  in  and 
near  cities  or  where  the  work  is  in  close  proximity  to  a  railroad, 
while  the  wooden  sheet-piling  will  be  cheaper  near  centers  of 
timber  supplies.  Steel-piling  will  also  show  more  economy  the 
greater  the  depth  of  cofferdam. 


CHAPTER  VII 
BOX  AND  OPEN  CAISSONS 

ART.  79.    DEFINITIONS  AND  CLASSIFICATION 

As  defined  in  the  Century  Dictionary,  a  caisson  is  a  "  large 
and  water-tight  box  or  casing,  in  which  work  is  conducted  below 
water-level,  as  in  a  bridge  pier."  Unfortunately  this  meaning 
is  true  only  for  a  small  proportion  of  the  structures  now  termed 
caissons.  In  fact,  so  many  modifications  of  the  original  type 
have  developed  that  further  differentiation  is  necessary.  For 
this  reason  caissons  will,  in  this  book,  be  divided  into  three 
general  types:  box  caissons,  open  caissons,  and  pneumatic 
caissons. 

All  caissons  have  one  characteristic  in  common:  they  form  a 
permanent  shell  for,  and  are  an  integral  part  of,  bridge  and  build- 
ing foundations,  being  used  simply  as  a  convenient  means  of 
placing  such  a  foundation  in  position. 

The  box  caisson  is  used  where  no  sinking  is  required,  and  con- 
sists merely  of  a  box,  open  at  the  top  and  closed  at  the  bottom, 
which  is  filled  with  concrete  or  other  masonry,  to  serve  as  a 
foundation  for  the  pier  or  other  structure  to  be  built  on  the  same. 
When  sinking  must  be  resorted  to  in  order  to  carry  the  founda- 
tion down  to  a  stratum  having  sufficient  bearing  power  to  carry 
the  superincumbent  load,  the  box  must  be  open  at  the  bottom 
in  order  that  the  earth  underneath  may  be  removed  to  allow 
sinking  to  take  place.  If  this  excavation  is  done  by  dredging 
through  the  water,  we  have  the  open  caisson,  while  if  the  caisson 
is  roofed  and  air  pressure  applied  to  fprce  out  the  water,  to  allow 
workmen  to  excavate  the  material  by  hand,  it  is  called  a  pneu- 
matic caisson.  Briefly  then,  a  caisson  is  a  box;  if  open  at  the 
top  and  closed  at  the  bottom,  it  is  a  box  caisson;  if  open  both 
at  the  top  and  at  the  bottom,  it  is  an  open  caisson;  while  if 

239 


240  BOX   AND   OPEN   CAISSONS  CHAP.  VII 

open  at  the  bottom  and  closed  at  the  top  and  utilizes  compressed 
air,  it  is  a  pneumatic  caisson.  In  all  cases  the  caisson  is  merely 
a  shell  which  must  be  filled  with  concrete  or  other  masonry  to 
form  the  foundation. 

Most  caissons  are  surmounted  with  cofferdams  on  account  of 
the  undesirability  of  extending  the  caisson  above  low  water-level 
both  for  reasons  of  durability  and  appearance. 

ART.  80.     Box  CAISSONS  or  TIMBER 

A  box  caisson  is  a  box,  usually  water-tight,  closed  at  the  bot- 
tom and  sides  and  open  at  the  top,  which  forms  an  integral  and 
permanent  part  of  the  foundation.  Box  caissons  are  made  of 
timber  and  of  concrete,  the  former  material  being  more  widely 
employed  than  the  latter. 

Except  where  placed  on  piles,  the  use  of  this  type  of  caisson  is 
limited,  owing  to  the  necessity  of  first  excavating  to  the  desired 
depth,  i.e.,  to  where  firm  bearing  may  be  obtained,  before  plac- 
ing the  caisson.  The  depth  to  which  it  is  possible  to  excavate  is 
limited  owing  to  the  tendency  of  the  wet  material  to  flow  into 
the  hole.  In  a  few  cases  box  caissons  have  been  made  to  sink 
several  feet  by  running  pipes  through  the  bottom  and  forcing 
water  through  the  same,  thus  washing  out  the  material  from 
underneath  and  allowing  sinking  to  take  place. 

The  box  caisson  used  for  the  foundation  of  the  Sutherland's 
River  bridge,  Nova  Scotia,  had  a  bottom  composed  of  a  double 
thickness  of  i2Xi2-inch  timbers  laid  close,  the  timbers  of  the 
upper  course  running  at  right  angles  to  those  of  the  lower  course. 
The  sides  were  formed  of  vertical  studding,  horizontal  sheathing 
and  diagonal  bracing.  This  caisson,  which  was  built  on  shore 
and  made  water-tight,  was  launched  and  towed  to  the  site,  after 
which  the  permanent  masonry  was  placed  to  sink  it  to  the  bed  of 
piles  on  which  it  was  to  rest. 

The  pivot-pier  caisson  of  the  Newark  Turnpike  Bridge 
between  Jersey  City  and  Kearney  Township,  was  circular  in 
plan  and  was  composed  of  light  wooden  walls,  with  an  octagona 
timber  grillage  4  feet  thick  for  the  bottom,  as  shown  in  Fig.  80  a. 


ART.  80 


BOX    CAISSONS    OF    TIMBER 


241 


1 6 


242  BOX  AND  OPEN   CAISSONS  CHAP.  VII 

This  caisson  rested  on  a  pile  foundation,  and  is  a  good  example  of 
a  box  caisson  resembling  a  movable  cofferdam  on  grillage.  The 
drawing  shows  that  a  small  amount  of  interior  bracing  was  used. 
The  caisson,  which  was  24  feet  high,  was  surmounted  above  low 
water-level  by  a  detachable  cofferdam  8  feet  high,  made  of  the 
same  material  as  the  sides  of  the  caisson. 

laThe  staves,  about  32  feet  long,  were  made  of  3  X  8-inch 
timbers,  dressed  and  cut  at  the  mill  to  the  required  dimensions. 
They  were  tapered  TT  inch,  to  correspond  with  the  batter 
of  the  pier  and  had  edges  beveled  to  make  exterior  caulking 
joints.  Each  stave  was  made  in  two  pieces  to  allow  for  the 
removal  of  the  cofferdam  on  top,  and  the  horizontal  butt  joint 
between  the  caisson  and  cofferdam  was  calked  on  the  outside. 
Each  stave  was  bored  at  the  mill  with  26  holes  for  f-inch 
spikes  to  the  inside  rings  made  of  two  courses  of  timber,  breaking 
joints,  bolted  together  and  having  their  outer  edges  dressed  to 
circular  curves.  At  eight  equidistant  points  on  the  upper  and 
middle  rings  pairs  of  horizontal  f-inch  connecting  plates  were 
bolted  to  them  projecting  inward  to  form  jaws  which  receive  the 
bolted  connections  of  the  12X1 2-inch  interior  braces .... 

"The  first  course  of  12X1 2-inch  grillage  timbers  was  assem- 
bled floating  in  the  river  and  a  pair  of  transverse  timbers  on  top 
of  it  were  bolted  to  the  outside  timbers.  These  acted  as  clamps, 
permitting  the  timbers  to  be  wedged  tightly  together  and  spiked 
to  the  second  course,  after  which  the  clamp  timbers  were 
removed  and  the  third  and  fourth  courses  laid  and  spiked  tightly 
together,  completing  the  grillage,  which  was  made  of  yellow  pine 
and  floated  with  the  upper  surface  about  14  inches  above  the 
water.  The  top-course  joints  were  caulked  with  oakum  and  a 
i2-inch  coaming  was  spiked  to  it,  and  caulked,  thus  increasing 
the  freeboard  and  providing  a  dry  working  platform  when  the 
grillage  was  submerged  deeper  by  men  and  materials.  The  bot- 
tom ring,  with  an  outside  radius  of  about  23^  feet,  was  made  of 
two  courses  of  3  X 1 2-inch  scarf  boards  concentric  with  the  pivot, 
and  was  spiked  to  the  grillage  with  yXi2-inch  dock  spikes. 
Inside  of  it  a  light  wooden  falsework  was  built  to  which  were 

1  Engineering  Record,  vol.  64,  page  720,  Dec.  16,  1911. 


ART.  8 1  BOX  CAISSONS  OF   CONCRETE  243 

secured  four  concentric  horizontal  rings,  each  made  with  two 
courses  of  6X1 2-inch  timber,  breaking  joints  and  dressed  to  cir- 
cular curves  on  the  outer  edges.  The  lowest  of  the  four  rings 
was  anchored  to  the  grillage  by  40  2^-inch  special  lag  screws 
penetrating  nearly  through  the  second  course  of  grillage.  The 
lower  sections  of  the  staves,  24  feet  long,  were  then  assembled  to 
the  rings  and  secured  to  them  by  four  f  X  7 -inch  spikes  in  each 
stave  at  each  ring.'7 

Caissons  of  a  somewhat  different  form  were  used  for  the  foun- 
dation of  the  south  pier  of  the  Duluth  Ship  Canal.  They  were 
from  24  to  36  feet  wide,  21  feet  high,  and  from  50  to  100  feet 
long.  The  floor  was  8  inches  thick  laid  close,  the  channel  side 
had  a  solid  wall  of  a  double  thickness  of  i2Xi2-inch  timbers, 
while  the  opposite  side  was  composed  of  a  single  thickness  of  1 2 
X 1 2-inch  timbers  laid  close.  Connecting  and  bracing  the  two 
walls  were  transverse  bulkheads  of  10X1 2-inch  material,  spaced 
4  feet  center  to  center  horizontally. 

The  caissons  were  built  in  the  harbor,  towed  to  the  site,  and 
sunk  by  filling  with  rock  and  gravel.  After  sinking,  the  cais- 
sons were  covered  with  a  layer  of  heavy  timbers,  on  which 
was  built  the  concrete  pier,  the  tip  of  the  caisson  being  slightly 
below  low  water-level. 

ART.  8 1.    Box  CAISSONS  or  CONCRETE 

The  two  principal  advantages  possessed  by  the  concrete  box 
caisson  over  the  timber  caisson  are:  First,  the  caisson  may  be 
carried  up  to  above  low  water-level,  thus  eliminating  cofferdam 
work;  and  second,  it  is  a  more  durable  type,  especially  in  those 
waters  infested  by  marine  wood  borers.  Caissons  made  of  con- 
crete will  usually  prove  somewhat  more  expensive  than  those 
made  of  timber. 

Fig.  Sia1  shows  the  type  of  caisson  used  as  breakwaters  and 
piers  for  a  bridge  forming  a  yacht  landing  at  Glen  Cove,  Long 
Island.  To  make  the  launching  easier  the  caissons  were  built 

in    two    sections.     They    were   reinforced    for   exterior   pres- 

i 

1  From  Paper  on  Reinforced  Concrete  Pier  Construction  by  EUGENE  KLAPP, 
Trans.  Am.  Soc.  C.  E.,  vol.  70,  page  448,  Dec.,  1910. 


244 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


sures  which  the  structures  would  meet  in  sinking  and  for  in- 
terior pressures  which  would  occur  at  low  tide  by  reason  of  the 
interior  filling. 

All  caissons  were  cast  standing  on  skids.     When  the  concrete 
hardened  sufficiently  a  derrick  scow  lifted  and  set  them  in  the 

t'To  be  Leveled  offer  Caisson  is  Placed 


Side  Wall  Reinforcement : 
Rods  placed  horizontally 

1%  'from  Surface  and  Spaced 
'  •  Indicated. 

'acts  placed 'vertically 
Spaced  J8"C.toC. 


V- 


'--  i  ""Rods  Spaced  12  "C.  to  C.both  ways. 
Vertical  Section  A-A. 


.  :.  '  r.tzS2SiX» 

y^zaav^Vj 

--•*-* 

4                    -> 

if'  ,«off 

)        j 

Diaphragms 

and  Anchored 
to5ideWat/,ai 

6K.;i        I 

Shown  ^ 

!                                 N-4s 

*       s  \ 
_Q>  ^ 

A  - 

i.  —  : 

--A 

Spacedsame 
asHor.Rods, 
\-l'6"long.   ) 

^?77rc-"-ra£; 

I     . 

va    ±_ 

Note:. 

All  8'x  12 "Caissons  to  be  Built  in 
Sections  the  Height  of  which  should 
not  exceed  10  ft  The  Reinforcement 
of  Bottom  Walls  and  Diaphragms 
will  be  same  as  Indicated  on  the 
Detail  of  12'*  12  'Caisson. 
The  Height  will  vary  as  Shown. 


r.r::cK:.'-''.'j'.::::j:r^°T^"rj"-jT'''''rx""--.i 

':  V 

N 

<"4"*24"  Dia- 
phragm in   ••! 
each  Section    \ 

,<^> 

^Q 


n'o"- 


•'-  .....  I2'0~ 
Horizontal  Section  B-B. 


Plan. 

12-Ft.x  12-Ft.  Caisson.  8~ftx  "^ Ft. Caisson. 

FIG.  8ia. — Box  Caisson  of  Reinforced  Concrete  near  Glen  Cove,   Long  Island. 

water,  after  which  they  were  towed  to  position  and  sunk.  Some 
of  the  upper  sections  were  placed  on  the  scow  and  lifted  directly 
from  there  upon  the  lower  sections  already  in  place.  In  the 


ART.  82  MISCELLANEOUS   TYPES       .  245 

bottom  sections  a  3 -inch  hole  was  cast,  which  was  closed  while 
the  caisson  was  being  towed  to  position.  When  directly  over  the 
site  of  the  foundation  bed,  water  was  let  in  by  unplugging  the 
hole  to  sink  the  structure,  after  which  the  same  was  filled  with 
sand  and  gravel. 

For  a  very  complete  discussion  of  the  subject  of  concrete  cais- 
son construction  for  breakwaters  the  reader  is  referred  to  a  paper 
by  Major  W.  V.  JUDSON  in  the  Proceedings  of  the  Western 
Society  of  Engineers,  vol.  14,  page  533.  An  abstract  of  this 
paper  may  be  consulted  in  Engineering  News,  vol.  62,  page  34, 
July  8,  1909. 

ART.  82.     MISCELLANEOUS  TYPES 

A  metal  box  caisson,  composed  of  a  vertical  cylinder  9  feet  in 
diameter  and  nearly  13  feet  high,  having  sides  formed  of  |-inch 
steel  plate  and  a  bottom  composed  of  a  ribbed  and  flanged  cast- 
ing, slightly  convex  downward,  was  sunk  about  13  feet  through 
quicksand  to  form  the  foundation  for  some  machinery  at  the 
General  Electric  Company's  Plant  at  Schenectady,  N.  Y. 
Through  the  bottom  there  were  forty -four  if -inch  holes,  each  hole 
being  tapped  for  a  vertical  pipe,  which  in  turn  was  connected 
to  a  3-inch  main  which  provided  water  at  80  pounds  pressure. 
Valves  were  so  placed  that  any  combination  of  streams  could  be 
used  at  once.  The  caisson  was  sunk  by  opening  the  valves,  thus 
forcing  the  water  through  the  pipes  to  scour  out  under  the  bot- 
tom of  the  cylinder.  At  the  same  time  the  caisson  was  heavily 
weighted  with  pig  lead.  Some  little  trouble  was  experienced  in 
keeping  the  caisson  plumb  but  by  using  certain  jets  at  certain 
times  and  by  placing  the  loading  material  mostly  on  the  high 
side  the  structure  was  finally  brought  to  bearing  on  the  firm 
material  The  pipes  were  then  disconnected  near  the  bottom 
and  concrete  placed  in  the  caisson. 

Another  modified  form  of  box  caisson  used  at  the  same  place 
to  avoid  danger  of  undermining  adjacent  structures  resting  on 
the  quicksand,  was  sunk  by  boring  out  the  quicksand  from  under 
the  caisson.  A  pile  foundation  was  to  be  used  and  as  it  was 
desired  to  cut  off  the  piles  at  an  elevation  well  below  ground 


246  .  BOX  AND  OPEN  CAISSONS  CHAP.  VII 

water -level,  a  box  caisson  4  feet  high  and  16  by  40  feet  in  plan, 
inside  dimensions,  was  constructed  with  a  large  number  of 
i2-inch  holes  cut  through  the  bottom.  Twelve-inch  vertical 
wrought-iron  pipes,  4  feet  long  and  open  at  both  ends,  were 
fitted  into  these  holes,  after  which  the  caisson  was  filled  with  con- 
crete to  the  top  of  the  pipes.  After  this  had  set  3600  tons  of  pig 
iron  were  loaded  on  the  caisson  between  the  pipes.  The  quick- 
sand would  not  rise  in  the  pipes  but  by  means  of  post-hole  augers 
the  material  was  raised  and  removed.  Care  was  taken  to 
remove  but  a  slight  amount  from  a  hole  at  any  one  time  in  order 
to  prevent  unequal  settlement.  After  sinking  the  desired 
amount,  about  4  feet,  piles  of  about  1 1  inches  diameter  at  the 
top  were  driven  through  the  pipes  to  a  distance  of  about  19 
feet  below  the  bottom  of  the  caisson  and  were  then  cut  off  level 
with  the  tops  of  the  pipes,  after  which  the  latter  were  grouted 
and  the  foundation  completed. 

In  both  the  foregoing  cases  the  problem  was  to  sink  a  founda- 
tion through  quicksand  without  disturbing  adjacent  structures 
founded  on  quicksand.  Success  was  due  to  weighting  the  cais- 
son so  heavily  that  quicksand  could  not  flow  under  the  same 
from  outside  and  at  the  same  time  providing  means  to  remove 
the  sand  under  the  caisson. 


ART.  83.    SINGLE- WALL  OPEN  CAISSONS 

An  open  caisson  is  a  box-like  self-contained  structure'  either 
partly  or  entirely  open  at  both  top  and  bottom,  and  forming  an 
integral  and  permanent  part  of  the  pier. 

The  open  caisson  which  forms  one  of  the  most  important 
classes  of  structures  used  for  subaqueous  work  and  has  the 
distinction  of  being  employed  for  the  deepest  foundations,  may 
be  divided  into  three  types:  First,  the  single-wall  timber  cais- 
son consisting  of  a  frame  with  solid  walls  and  without  top, 
bottom,  interior  chambers,  or  cutting  edges;  second,  the  cylin- 
der caisson  consisting  of  open  cylinders  of  iron  or  masonry; 
and  third,  the  caisson  with  dredging  wells  consisting  of  a  struc- 
ture partly  closed  both  at  the  top  and  at  the  bottom,  with  open 


ART.  83  SINGLE- WALL   OPEN   CAISSONS  247 

wells  running  vertically  through  it.  The  first  type  is  used  where 
little  or  no  sinking  is  required,  while  the  second  and  third  are 
employed  where  sinking  is  necessary;  the  second  where  the 
required  cross-sections  of  foundations  are  small  and  the  third 
where  they  are  large. 

In  the  details  of  construction  the  single-wall  open  caisson  of 
timber  resembles  the  single- wall  crib  cofferdam  (Art.  72)  and 
differs  from  it  chiefly  in  that  it  is  an  integral  part  of  the  founda- 
tion. The  caisson  usually  consists  of  a  solid  framework  of 
12X1 2-inch  timbers  thoroughly  caulked.  It  is  used  only  where 
little  or  no  sinking  is  required  or  else  where  the  material  to  be 
sunk  through  is  very  soft.  This  is  true  since  sinking  must  be 
done  by  artificially  weighting  the  structure  with  removable 
material,  such  as  iron  rails.  If  soft  material  covers  the  site,  as 
much  of  it  as  possible  should  be  dredged  out  before  placing  the 
caisson.  Removing  the  material  from  within  the  caisson  after  it 
is  placed,  and  also  using  the  water-jet  along  the  sides  will 
greatly  facilitate  sinking.  On  reaching  its  final  position  con- 
crete is  deposited  through  the  water  to  a  depth  of  several  feet 
and  allowed  to  harden.  This  virtually  forms  a  box  caisson 
which  is  then  pumped  out  and  filled  with  concrete,  placed  in  the 
dry,  to  make  the  foundation  for  the  pier.  It  is  customary  to 
add  a  cofferdam  on  top  of  the  caisson  so  that  the  latter  may  not 
extend  above  low  water. 

Fig.  83 a  shows  the  details  of  the  caisson  used  for  one  of  the 
piers  of  the  French  River  bridge  of  the  Canadian  Pacific  Rail- 
way. The  lower  part  was  built  on  shore,  the  structure  then 
being  launched  and  completed  in  the  river.  Rolls  of  canvas 
were  attached  to  the  inner  faces  along  the  bottom  and  as  soon 
as  the  caisson  was  lowered  to  the  bottom,  divers  went  down  and 
spread  out  the  canvas,  and  on  it  laid  bags  of  cement  to  close 
the  openings  under  the  walls.  A  layer  of  mortar  was  then  de- 
posited through  the  water  on  the  rock  bottom,  after  which  the 
remainder  of  the  caisson  was  filled  with  concrete.  The  cais- 
son was  surmounted  with  a  cofferdam  of  exactly  the  same 
construction  as  the  caisson. 

Fig.  836  shows  the  details  of  the  caissons  used  in  the  substruc- 


248 


BOX   AND    OPEN   CAISSONS 


CHAP.  VII 


ture  of  the  Columbia  River  bridge  of  the  Oregon- Washing  ton 
Railroad  &  Navigation  Co.  The  river  bed  was  composed  of 
very  firm  soapstone,  overlaid  in  places  with  cemented  boulders, 


v— 

30  0   -> 

(  1  Cement 
\  3  Sand 
(  S  Rock 

H-Kl  t-ftl-  17-H  

III          1 1 


Sectional  Side  Elevat 


4*9 


xlO 


Sectional 
End  Elevation. 


25-  2**  6'0'S 

<3T(?  ^A/'/fea'  J 

Projecting  3' up  into  Concrete,      cvj 


Sectional  Plan. 
FIG.  830. — Open  Caisson  for  Canadian  Pacific  Railway  Bridge  over  French  River. 

gravel  and  sand.  The  maximum  depth  of  water  at  the  usual 
stage  of  the  river  was  about  30  feet,  with  a  maximum  velocity 
of  current  of  7  miles  per  hour. 


ART.  83 


SINGLE-WALL   OPEN   CAISSONS 


249 


The  caissons  after  being  framed  were  floated  to  place  and 
sunk  by  loading  with  steel  rails,  the  latter  being  placed  in  the 
racks  shown  on  the  drawings.  All  concrete  was  placed  through 
the  water,  no  attempt  being  made  to  pump  out  the  caisson. 
Upon  completion  of  concreting  all  timbers  above  low  water- 
level  were  removed. 

Some  of  the  piers  of  the  Fraser  River  bridge  at  New  West- 
minster, British  Columbia,  were  founded  on  caissons,  14  by 


Cross    Section. 


1  Side     Elevation.  |~| 

7 

Plan. 

-\ 

'  u          u 

FIG.  836. — Open  Caisson  for  Piers  of  Oregon- Washington  Railroad  and  Navigation 
Company  over  Columbia  River. 

34  feet  in  plan,  resting  on  pile  foundations,  in  which  the  piles 
were  60  feet  long.  These  caissons  were  composed  of  i2X 
i2-inch  timbers.  They  were  sunk  to  a  depth  of  from  10  to  20 
feet  below  the  original  level  of  the  bottom  by  loading  stones  on 
timbers  placed  across  their  tops  and  by  pumping  out  the  soft 
material  with  the  sand  and  mud  pump  described  in  Art.  91. 
On  reaching  the  final  position  a  layer  of  1-2-3  concrete,  5  to 


250 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


10  feet  thick,  was  deposited  around  the  piles  by  a  steel-pipe 
tremie.     This  concrete  was  allowed  to  harden  one  week,  after 


Section  through 
Course  3 or  5 


Top  View 


Section  A-A 


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Half  Elevation  Half  Vertical  Section 

FIG.  83*;. — Basket  Crib  Type  of  Open  Caisson. 

which  the  caisson  was  pumped  out  and  the  piles,  which  were 
driven  previously  to  placing  the  caisson,  were  then  cut  off  5  feet 
below  low  water,  the  top  of  the  caisson  being  2  feet  below  low 


ART.  84  CYLINDER  CAISSONS  251 

water.  The  remainder  of  the  concrete  was  laid  in  the  dry. 
The  chief  function  of  the  caisson  was  to  protect  the  upper  19 
feet  of  the  piles  against  scour.  The  physical  conditions  at  the 
site  are  described  in  Art.  88. 

To  sink  the  caissons  of  the  Rio  Conchos  bridge  of  the  Kan- 
sas City,  Mexico  &  Orient  Railway,  stringers  were  placed  across 
the  ends  and  a  floor  was  placed  on  the  portions  of  these  stringers 
projecting  beyond  the  sides,  and  these  floors  were  boxed  up  to  a 
height  sufficient  to  carry  a  load  of  75  tons  of  gravel  each.  This 
gravel  was  dredged  from  the  inside  of  the  caissons. 

Fig.  83  c  illustrates  an  example  of  the  circular  caisson  of  a  form 
called  the  basket  crib.  This  type  of  caisson  has  been  used  by 
the  Engineering  Department  of  Boston,  Mass.,  in  a  number  of 
cases  for  the  foundations  of  pivot  piers.  This  caisson,  which 
was  60  feet  in  diameter  and  30  feet  high,  is  of  special  interest  on 
account  of  the  cylindrical  chamber,  30  feet  in  diameter  and  22 
feet  high,  in  the  upper  part  of  the  caisson,  which  reduced  the  vol- 
ume of  concrete.  This  plan  follows  the  tendency  of  the  present 
day  in  regard  to  bridge  piers  (Chapter  XII).  luThe  basket 
crib,  or  form  for  the  pier  foundation,  was  built  of  about  145 
horizontal  courses  of  3Xi2-inch  yellow  pine  planks,  8  feet  long, 
laid  flat  and  breaking  joints.  The  ends  were  beveled  to  make 
radial  joints,  and  each  plank  was  secured  to  those  below 
it  by  i-inch  oak  tree  nails  9  inches  long,  two  at  each  end  of  each 
plank.  ...  In  addition  the  planks  were  well  spiked  to  the 
lower  courses  throughout  their  entire  length  with  6-inch  spikes. 
The  courses  were  also  secured  together  by  4  Xi  2-inch  vertical 
planks  opposite  alternate  joints  which  were  fastened  to  the  inner 
circles  of  the  crib  by  lag  screws." 

Before  placing  the  caisson  the  site  was  dredged  to  rock. 
The  caisson  was  sunk  by  loading  with  old  iron  and  stone  and  by 
hanging  heavy  chains  over  the  walls. 

ART.  84.     CYLINDER  CAISSONS 

The  cylinder  caisson  consists  of  a  cylindrical  shell  of  masonry, 
wood,  iron,  or  reinforced  concrete,  shod  with  some  form  of  cut- 

1  Engineering  Record,  vol.  68,  page  138,  Aug.  2,  1913. 


252  BOX  AND   OPEN   CAISSONS  CHAP.  VII 

ting  edge,  and  is  sunk  by  excavating  the  material  within  the  cais- 
son and  at  the  same  time  weighting  it,  or  using  the  water-jet 
around  the  sides  to  decrease  the  friction.  Where  the  cylinder 
is  of  large  diameter  there  may  be  two  shells,  an  outer  and  an 
inner  one,  the  space  between  the  two  being  filled  with  concrete 
as  the  caisson  sinks.  Where  the  cylinder  caisson  is  used  it  is 
customary  to  construct  the  piers  as  an  upward  extension  of 
the  caisson. 

This  type  of  foundation  is  widely  employed  where  the  loads 
to  be  supported  are  not  great  but  where  it  is  necessary  to  go 
down  a  considerable  distance  to  avoid  scouring  action.  Particu- 
larly in  the  British  Provinces  of  the  Far  East  has  it  been  widely 
used,  for  there  the  rivers  are  dry  or  nearly  so  for  a  large  part  of 
the  year,  but  deep  and  torrential  during  certain  months,  thus 
requiring  the  foundations  to  be  bedded  at  a  depth  below  that 
of  any  possible  scour. 

CYLINDER  CAISSONS  OF  MASONRY. — For  many  centuries  the 
natives  of  East  India  have  employed  the  masonry  caisson,  or 
1  open  well,'  as  it  is  more  frequently  called,  in  sinking  the  founda- 
tions for  their  bridges.  In  their  most  primitive  form  these 
caissons  consisted  of  wells  large  enough  for  but  one  man  to  work 
in — about  3  feet  in  diameter — and  were  built  of  brick  masonry 
resting  on  wooden  curbs.  They  were  sunk  to  a  maximum  depth 
of  about  17  feet  by  divers  excavating  inside  of  them  and  bring- 
ing up  the  excavated  material  in  buckets.  When  bedded  on  a 
firm  stratum  they  were  filled  with  masonry.  For  those  streams 
which  were  low  or  dry  for  much  of  the  year  this  was  a  cheap 
and  effective  method  of  placing  the  foundations. 

A  modern  example  of  this  general  type  is  found  in  the  con- 
struction of  the  north  abutment  caissons  of  the  Chittravati 
bridge,  where  brick  caissons  on  wrought-iron  curbs  were  used, 
the  exterior  diameter  being  12  feet  and  the  thickness  of  the 
brick  wall  2  feet.  They  were  sunk  to  a  maximum  depth  of 
about  63  feet  by  dredging  through  the  wells  and  by  loading 
with  iron  rails. 

CYLINDER  CAISSONS  OF  WOOD. — Fig.  840  illustrates  the  cais- 
sons of  wood  used  for  the  foundations  of  a  shipping  pier  at  San 


ART.  84 


CYLINDER    CAISSONS 


253 


Francisco.  Each  caisson  was  made  of  Douglas  fir  timber  staves 
4  inches  thick,  banded  with  iron.  The  bottom  consisted  of  a 
cast-iron  bell  attached  to  the  staves  as  shown  in  the  diagram. 
The  cylinders  were  bedded  about  12  inches  in  a  hard  clay 
stratum  which  was  about  40  feet  below  mean  low  water  and  46 
feet  below  mean  high  water.  An  average  depth  of  about  15  feet 
of  soft  mud  overlaid  the  clay. 

The  caissons  were  sunk  through  this  soft  material  by  means 
of  four  water- jets  playing  around  the  bottom  of  each.     Little 


Detail  of  C.I.  Bell. 


Cylinder  Reinforcement. 


FIG.  84a. — Cylinder  Caisson  for  Foundations  of  Shipping  Pier  at  San  Francisco,  Cal. 


driving  was  necessary  until  the  clay  stratum  was  reached. 
Special  frames  were  used  on  top  of  the  caissons  to  receive  the 
blows  of  the  hammer.  As  soon  as  the  desired  penetration  was 
obtained  the  water  and  mud  were  pumped  from  the  caisson — the 
clay  effectually  sealing  the  bottom — and  the  bottom  carefully 
inspected,  after  which  the  reinforcement  was  placed  and  the 
cylinder  filled  with  1-2-4  concrete.  This  type  of  caisson  has 
been  used  but  little  on  account  of  its  lack  of  strength  and  rather 
high  cost. 


254  BOX  AND  OPEN  CAISSONS  CHAP.  VII 

ART.  85.     METAL  CYLINDER  CAISSONS 

Experience  has  shown  that  there  are  many  advantages  gained 
by  using  a  shell  of  iron  or  steel  in  place  of  one  of  brick  masonry, 
especially  when  water  covers  the  site  of  sinking.  The  shell  may 
be  of  cast  iron,  wrought  iron  or  steel,  the  last  being  used  almost 
exclusively  in  this  country.  There  are  three  advantages  which 
the  metal  type  possesses  over  the  masonry:  First,  greater 
strength;  second,  a  higher  degree  of  water- tightness;  and 
third,  less  friction  developed  in  sinking.  After  the  caisson  is 
sunk  to  a  proper  bearing  it  is  filled  with  concrete  or  sand;  the 
former  being  invariably  used  in  America,  while  English  engineers 
use  the  latter  to  a  considerable  extent. 

The  California  City  Point  coal  pier  offers  a  good  example  of 
the  use  of  cylinder  caissons  of  small  diameter,  being  formed  of 
flanged  cast-iron  pipe  4  feet  in  diameter.  The  depth  of  water  at 
the  site  was  about  30  feet,  while  from  4  to  40  feet  of  mud  over- 
laid the  hard  bottom  on  which  the  caissons  were  to  rest. 

In  order  to  increase  the  bearing  area  on  the  bottom  a  special 
conical  section  was  made  for  the  lower  end  of  the  cylinders,  the 
maximum  diameter  of  this  section  being  8  feet.  The  shell  above 
this  lower  section  was  composed  of  regular  4-foot  cast-iron  pipe 
in  i2-foot  lengths,  each  section  being  fastened  to  the  one  above 
and  below  with  forty-four  if-inch  bolts  through  the  flanges. 

Sinking  the  shells  was  accomplished  as  follows:  A  number  of 
sections  were  bolted  together,  lowered  vertically  to  position  on  the 
mud  bottom,  and  braced  there  with  guys.  They  were  sunk  by 
dredging  out  the  inside  of  the  pipe  by  means  of  a  |-cubic  foot 
orange-peel  bucket,  new  sections  of  pipe  being  added  as  the 
cylinder  went  down.  Where  the  resistance  to  sinking  was  con- 
siderable the  work  was  facilitated  by  temporarily  loading  the  top 
of  the  caisson  with  steel  beams  and  girders,  and  by  the  use  of  the 
water-jet  around  the  cutting  edge.  After  sinking  operations 
were  completed  the  conical  portion  of  the  cylinder  was  filled 
with  concrete  deposited  through  the  water,  and  after  the  latter 
had  hardened  the  water  was  pumped  from  the  cylinder.  Four- 
teen vertical  reinforcing  rods  of  ifVinch  diameter  were  then 


ART.  85  METAL   CYLINDER   CAISSONS  255 

placed  in  each  cylinder,  after  which  the  latter  was  filled  with  a 
1-3-5  mixture  of  concrete,  rammed  in  1 2-inch  layers,  to  form  the 
foundation  for  one  of  the  columns  of  the  coal  pier. 

The  caissons  for  the  highway  bridge  across  the  Kansas  River 
at  Fort  Riley  are  typical  examples  of  steel  cylinder  caissons,  so 
much  used  for  light  highway  bridges,  where  it  is  necessary  to  go 
down  some  distance  below  the  bed  of  the  stream  to  get  proper 
bearing  material.  Each  pier  consisted  of  two  cylinders  well 
braced  together,  each  cylinder  being  5  feet  in  diameter.  The 
metal  used  was  J  inch  thick,  although  a  thickness  of  f  inch 
would  have  been  better.  The  cylinder  sections  were  in  6-foot 
lengths,  butt- jointed  with  splice  plates  on  the. inside,  and  were 
riveted  up  in  12-  and  i8-foot  sections  in  the  bridge  shop.  The 
cylinders  were  54  feet  long  and  were  sunk  through  fine  sand  by 
dredging  and  weighting,  and  at  a  time  when  the  river  was  dry,  to 
an  average  depth  of  24  feet  below  the  river  bottom. 

The  8-foot "  diameter  cylinders  used  on  the  Atchafalaya 
bridge,  Morgan  City,  La.,  are  said  to  be  the  deepest  single- wall 
cylinder  caissons  on  record,  being  sunk  to  a  depth  of  120  feet 
below  high  water,  or  from  70  to  115  feet  below  the  mud  line. 
Below  this  mud  line  the  cylinders  were  of  cast  iron  and  above  of 
wrought  iron  (see  BAKER'S  Masonry  Construction). 

English  engineers  have  used  cast-iron  cylinder  caissons  of 
fairly  large  diameter  for  many  of  their  bridges,  but  experience 
(Charing  Cross  bridge,  1860)  long  ago  taught  them  that  the 
lower  sections  should  be  of  wrought  iron  or  steel,  for  cast  iron  is 
too  brittle  a  material  to  use  for  a  cutting  edge.  For  a  very 
complete  description  and  discussion  of  the  sinking  of  cast-iron 
cylinder  caissons  with  wrought-iron  cutting  edges,  see  Proceed- 
ings of  the  Institution  of  Civil  Engineers,  vol.  103,  page  135. 

One  of  the  most  expensive  items  connected  with  the  sinking 
of  cylinder  caissons  is  that  of  artificially  weighting  the  structure 
to  promote  sinking,  because  this  weighting  material  must 
be  removed  and  replaced  each  time  new  sections  are  added 
to  the  caisson.  Largely  for  this  reason,  where  the  size  of  the 
caisson  will  permit,  it  is  advisable  to  use  a  double  wall  so  that 
much  of  the  permanent  concrete  filling  may  be  placed  during 


256 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


each+afdrwrnf.^ 
andateachdft.  ^      <, 
vert  SpLPK    ^\    \  Spl.ff6timpf\ 


I  "C.5.  Rivets  on  Outs.af Band 
Part  Elevation. 


FIG.  850.— Details  of  Open  Caisson  for  Pivot  Pier  of  Omaha  Interstate  Bridge. 

Designed  in  1902. 


ART.  86         REINFORCED-CONCRETE   CYLINDER  CAISSONS  257 

sinking,  and  thus  decrease  the  amount  of  temporary  loading 
necessary. 

This  was  done  in  the  caisson  for  the  pivot  pier  for  the 
Omaha  Bridge  &  Terminal  Company's  bridge  across  the  Missouri 
River  from  East  Omaha  to  Council  Bluffs,  la.  As  shown  in 
Fig.  850  the  caisson,  which  was  of  steel,  had  an  outer  diameter  of 
40  feet  and  an  inner  diameter  of  20  feet.  It  rested  on  solid  rock 
1 20  feet  below  low  water.  For  the  first  50  feet  the  material  was 
sand  and  clay,  and  below  this  there  was  about  60  feet  of  coarse 
sand  overlying  a  few  feet  of  boulders  which  rested  on  solid  rock. 
At  a  low  stage  of  the  river  the  depth  of  water  was  slight.  Sink- 
ing was  accomplished  by  a  combination  of  three  agencies: 
Dredging  the  material  from  inside  the  caisson,  using  water-jets 
to  reduce  the  side  friction,  and  filling  the  space  between  the  two 
shells  with  concrete.  On  completing  the  sinking  the  well  was 
also  filled  with  concrete.  The  details  of  the  caisson  are  clearly 
shown  in  the  illustrations. 

In  the  Pyrmont  Bridge,  Sidney,  N.  S.  W.,  the  same  general 
type  of  caisson  as  just  described  was  used,  except  that  the  shell 
was  of  wrought  iron  instead  of  steel.  For  details  of  this  work  see 
Proceedings  Institution  of  Civil  Engineers,  vol.  170,  page  138. 

ART.  86.     REINFORCED- CONCRETE  CYLINDER  CAISSONS 

The  use  of  reinforced  concrete  for  this  type  of  caisson  is  likely 
to  increase  greatly  in  the  future,  since  it  is  the  most  appropriate 
material  as  explained  in  Art.  90. 

One  of  the  early  examples  in  America  of  the  application  of  this 
type  of  caisson  was  placed  in  1910  in  the  foundations  of  the  ped- 
estals for  the  Penhorn  Creek  Viaduct  of  the  Erie  Railroad. 
A  single  caisson  was  used  for  each  pedestal.  The  shell  of  the 
caisson  consisted  of  a  hollow  reinforced- concrete  cylinder,  hav- 
ing an  exterior  diameter  of  6J  feet  and  an  interior  diameter  of 
4§  feet,  thus  giving  a  thickness  of  i  foot.  It  was  reinforced  with 
f -inch  vertical  rods,  spaced  9  inches  center  to  center,  and  by  J- 
inch  horizontal  circular  rods  spaced  6  inches,  the  former  located 
2  inches  from  the  outside  face  and  the  latter  just  inside  of  these. 
17 


BOX  AND   OPEN   CAISSONS 


CHAP.  VII 


The  depths  to  which  the  caissons  were  sunk  varied  greatly, 
many  of  them  extending  to  about  70  feet  below  the  surface 
of  the  ground,  which  corresponds  to  about  55  feet  below  ground 
water-level. 

In  constructing  a  caisson  a  pit  about  n  feet  square  and  10 
feet   deep   was   excavated   and   lined   with   3Xi2-inch   butt- 


Plan. 

—  -__  ^--—  "—•  "  —  "-—  —  1 

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Vertical        Section. 
FIG.  86a. — Cutting  Edge  of  Caisson,  Penhorn  Creek  Viaduct,  Jersey  City,  N.  J. 

jointed  sheathing,  braced  by  i2Xi2-inch  horizontal  rangers. 
Four  vertical  i2Xi2-inch  sticks  were  then  placed,  one  at  the 
middle  of  each  waling  piece,  to  serve  as  a  guide  for  the  caisson. 
The  cast-iron  cutting  edge  shown  by  the  heavy  lines  in  Fig.  860, 
was  then  placed  in  the  bottom  of  the  pit.  Above  this  were 
placed  outside  and  inside  collapsible  steel  forms  in  5-foot  lengths. 
All  caissons  were  cast  in  20-foot  units,  the  caisson  being  built 
to  this  height,  allowed  to  set,  sunk,  and  another  section  added. 


ART.  86.        REINFORCED-CONCRETE  CYLINDER  CAISSONS  259 

the  whole  operation  being  repeated  until  the  desired  depth 
was  reached.  Each  section  was  allowed  to  harden  six  days  be- 
fore it  was  sunk. 

Sinking  through  the  mud  and  sand  was  effected  for  the  most 
part  by  interior  excavation  with  an  orange-peel  bucket.  The 
water-jet  was  used  to  some  extent  and  weighting  was  also 
resorted  to  at  times.  It  was  found  advantageous  to  keep  the 
jet  pipes  separate  from  the  caisson  and  to  work  them  by  hand. 
The  average  rate  of  sinking  through  mud  was  6|  feet  per  day, 
while  through  the  dense  underlying  sand  only  about  ij  feet  per 
day  could  be  accomplished. 

It  was  at  first  intended  to  found  the  caissons  on  rock,  using 
an  allowable  bearing  pressure  of  10.8  tons  per  square  foot,  but 
later,  owing  to  the  greater  depth  of  the  rock,  it  was  decided 
to  found  them  on  the  dense  sand  above,  which  it  was  thought 
would  safely  bear  a  load  of  7  tons  per  square  foot.  In  order  to 
reduce  the  unit  pressure  to  this  amount  the  bottom  was  belled 
out  as  shown  in  the  illustration.  The  conical  or  belled  section, 
which  consisted  of  a  number  of  TV-inch  steel  plates,  was  placed 
by  a  diver  who,  with  the  aid  of  a  water-jet  forced  the  dense 
sand  from  around  the  cutting  edge  and  placed  the  plates.  Each 
plate  was  forced  into  the  sand  a  slight  distance  at  the  bottom 
and  sprung  behind  the  cutting  edge  at  the  top.  Upon  the  com- 
pletion of  this  work  the  caisson  was  filled  with  1-2^-5  concrete. 

Another  interesting  application  of  reinforced- concrete  cylin- 
der caissons  is  that  for  the  foundation  of  the  lumber  dock  at 
Balboa,  Canal  Zone,  the  details  of  which  are  shown  in  Figs.  S6b 
to  e  inclusive. 

laThe  bottom  section  forms  a  footing,  and  differs  from  the 
others  in  that  the  exterior  surface  is  shaped  like  the  frustum  of 
a  cone.  The  base  of  the  footing  rests  on  a  shoe  made  up  of 
steel  plates,  as  shown  in  Fig.  86  b.  The  inside  form  (Fig.  S6c) 
is  wedged  tightly  against  the  upper  edges  of  the  diagonal  plates 
of  the  shoe,  and  when  the  concrete  is  poured,  the  mixture  fills 
only  that  portion  of  the  shoe  bounded  by  the  outer  vertical  plate 
and  the  diagonals.  In  this  way,  a  circular  wedge-shaped  cutting 
edge  of  steel  is  formed,  entirely  protecting  the  concrete." 

Engineering  Record  vol.  66,  page  60,  July  20,  1912. 


260 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


r - 


ART.  86          REINFORCED-CONCRETE    CYLINDER   CAISSONS 


261 


3 Spaces® /2t 
-J-<'</-fS/ 


TransverseTIes 
"s  Hoops  £'aBars 


At  first  the  caissons  were  built  in  place  like  those  of  the  Pen- 
horn  Creek  Viaduct,  but  the  work  progressed  so  slowly,  due  to 
having  to  work  in  a  cramped  space,  that  the  concrete  was  later 
cast  in  6-foot  sections  away  from  the  site. 

laThe  6-foot  cylindrical  sections  are  molded  on  a  platform 
for  the  purpose,  and  lowered  by  cranes  into  position  at  the  proper 
time.  The  reinforcing  scheme  consists  of  a  series  of  inner  and 
outer  vertical  rods  to  which  are  bound  a  series  of  inner  and  outer 
horizontal  rings.  In  con- 
structing the  sections,  the 
vertical  reinforcement  must 
be  interrupted  near  the  sec- 
tion joints,  but  strength  is 
given  by  means  of  six  i-inch 
steel  anchor  rods,  12  feet  in 
length,  which  are  passed 
through  cores  molded  in  the 
shell.  A  joint  between  rods 
thus  comes  in  every  other 
section  only.  The  rods  are 

connected  by  sleeve  nuts,  which  are  fitted  just  above  a  sec- 
tion joint  and  a  small  wedge-shaped  niche  is  molded  on  the 
outside  of  the  shell  of  necessary  sections  for  the  purpose  of  ad- 
justing and  fitting  the  junction  of  the  rods.  Fig.  86J,  which 
shows  the  method  of  construction,  indicates  sections  but  3  feet 
in  height,  but  this  was  modified  as  described." 

The  material  sunk  through  was  silt,  sand,  and  clay,  in  the 
order  named,  overlying  bedrock  which  was  from  60  to  70  feet 
below  the  surface.  Little  or  no  water  covered  most  of  the  site. 
For  the  most  part  the  caissons  were  sunk  by  laborers  excavating 
inside  of  them;  the  water  was  kept  down  by  pumping,  and  the 
spoil  was  lifted  out  with  buckets  of  5  cubic  feet  capacity.  When 
rock  was  reached  the  cutting  edge  was  embedded  about  i  foot 
in  the  same,  after  which  a  conical  depression  was  blasted  out  of 
the  rock  in  the  center  in  order  to  have  the  concrete  filling 
form  a  strong  bond.  After  this  the  cylinder  was  filled  with 

1  Engineering  Record,  vol.  66,  page  60,  July  20,  1912. 


LongitudmalTies 


FIG.  86e. 


262  BOX   AND   OPEN   CAISSONS  CHAP.  VII 

a  1-3-5  mixture  of  concrete.     The  shells  themselves  were  con- 
structed with  a  1-2-4  mixture. 

ART.  87.     OPEN  CAISSONS  WITH  DREDGING  WELLS 

The  type  is  based  on  the  same  principle  as  the  double- wall  open- 
cylinder  caisson,  differing  from  the  latter  only  in  the  matter  of 
shape  and  size;  some  open-cylinder  caissons  may  be  as  large  as 
those  to  be  classified  under  the  head  of  open  caissons  with  dredg- 
ing wells.  Perhaps  the  most  notable  difference  lies  in  the  fact 
that  the  open-cylinder  caisson  has  but  one  dredging  well,  while 
the  type  to  be  treated  in  this  and  the  three  following  Articles 
always  has  more  than  one. 

The  open  caisson  with  dredging  wells  is  a  type  of  construction 
which  has  been  employed  for  the  deepest  foundations  ever 
used  for  bridge  piers.  Theoretically  there  is  no  limit  to  the 
depth  to  which  this  class  of  caissons  may  be  sunk.  The 
essential  principle  of  the  construction  is  a  box-like  structure  of 
wood,  iron,  or  reinforced  concrete,  with  ballast  pockets  in  the 
same  and  with  open  wells  running  vertically  through  it,  these 
wells  flaring  out  at  the  bottom  to  practically  the  whole  area  of 
cross-section  of  the  caisson.  Through  the  wells,  by  means  of 
dredges,  the  material  is  excavated  from  the  bottom,  and  this, 
together  with  simultaneously  filling  the  pockets  with  concrete, 
is  usually  sufficient  to  sink  the  structure.  As  in  the  other 
forms  of  caissons,  when  the  structure  is  sunk  to  good  bearing 
material  the  wells  are  filled  with  concrete. 

The  great  advantage  of  this  type  of  structure  for  foundations 
is  that  all  the  work  is  done  above  water,  so  that  the  cheapest 
class  of  labor  can  be  employed,  thus  under  favorable  conditions 
making  a  very  economical  foundation.  In  the  use  of  the  open 
caisson  method  there  are  three  disadvantages,  which  are  absent 
in  either  the  cofferdam  or  the  pneumatic  caisson  process.  They 
are  as  follows:  First,  the  character  of  the  bottom  on  which  the 
caisson  finally  rests  can  never  be  as  satisfactorily  known  as  when 
it  is  possible  to  exclude  the  water  and  inspect  the  bottom  in  the 
dry,  nor  can  the  latter  be  leveled  and  cleaned  as  easily  as  when 


ART.  88  CONSTRUCTION   WITH   TIMBER  263 

the  other  methods  are  employed;  second,  the  concrete  which  is 
placed  in  the  bottom  of  the  well  must  be  placed  through  the 
water  and  consequently  is  not  as  good  concrete  as  when  placed 
in  the  dry;  and  third,  it  is  difficult  to  estimate  the  possible  rate  of 
sinking  owing  to  the  trouble  which  boulders  and  sunken  logs 
will  offer  when  encountered  under  the  cutting  edge.  In  spite 
of  these  disadvantages  the  open  caisson  with  dredging  wells 
is  widely  employed  for  depths  greater  than  can  be  satisfactorily 
handled  by  the  cofferdam  process  and  where  the  cost  of  the  pneu- 
matic caisson  process  prohibits  its  use,  or  where  the  depth  is 
greater  than  no  feet  below  water-level,  the  limiting  depth  in 
practice  for  pneumatic  caisson  work. 

Since  the  sinking  of  caissons  with  dredging  wells  is  not  under 
thorough  control,  the  caissons  should  always  be  made  large 
enough  to  allow  a  moderate  amount  of  deviation  from  the  cor- 
rect position.  As  the  wells  or  dredging  tubes  are  the  chief 
means  by  which  the  descent  can  be  regulated  as  regards  direc- 
tion, these  should  be  so  placed  as  to  facilitate  this  object.  For 
instance,  when  one  end  of  the  caisson  strikes  soft  material  and 
consequently  sinks  faster  than  the  other  end,  the  caisson  can  be 
brought  back  to  a  vertical  position  by  dredging  solely  from  the 
high-end  well;  but  on  the  other  hand,  if  the  wells  are  distributed 
along  the  longitudinal  center  line,  as  was  the  case  in  the  Hawkes- 
bury  bridge  caissons  (Art.  83),  and  Fraser  River  bridge  cais- 
sons (Art.  88),  and  one  side  strikes  softer  material  than  the 
other  side  it  becomes  a  difficult  matter  to  keep  the  structure 
from  tilting.  A  better  arrangement,  consisting  of  two  longitu- 
dinal rows  of  wells,  was  used  in  the  Willamette  River  bridge 
caissons  (Art.  88). 

ART.  88.     CONSTRUCTION  WITH  TIMBER 

In  America  the  pneumatic  form  of  caisson,  although  more 
expensive,  has  been  preferred  to  the  open  caisson;  but  for  the 
relatively  small  number  of  the  latter  that  have  been  used, 
because  of  the  low  cost  of  timber,  the  wooden  type  has  been 
employed  in  most  cases.  In  addition  to  the  advantage  of  low 


264  BOX  AND   OPEN  CAISSONS  CHAP.  VII 

cost,  the  wooden  type  is  easily  built  and  makes  a  strong  and 
elastic  caisson. 

Fig.  8Sa  shows  the  details  of  the  deepeat  caisson,  that  for 
Pier  4  of  the  Fraser  River  bridge  at  New  Westminster,  British 
Columbia.  This  caisson  was  of  timber,  and  was  sunk  to  a  depth 
of  135  feet  below  water-level.  The  outside  walls  were  built  of 
solid  courses  of  12X1 2-inch  timber,  sheathed  on  the  outside 
with  vertical  2-inch  planks.  These  walls  were  built  on  a  solid 
triangular-shaped  timber  base  of  twelve  courses  of  material,  the 
inside  of  this  base  also  being  sheathed  with  2-inch  planks.  The 
dredging  wells  were  framed  with  both  longitudinal  and  trans- 
verse timbers,  laid  solid  near  the  bottom  but  open  above  this, 
and  sheathed  with  2-inch  material.  The  outer-  and  well-wall 
timbers  formed  a  series  of  pockets  which  were  filled  with  con- 
crete during  the  sinking  of  the  caisson.  All  the  seams,  both 
in  the  horizontal  timbers  and  vertical  sheathing,  and  in 
the  upper  two  courses  of  the  solid  timber  base,  were  thor- 
oughly caulked. 

The  caisson  was  built  to  a  height  of  about  14  feet  on  ways  on 
the  shore,  and  then  launched  and  towed  to  the  site  where  it  was 
to  be  sunk.  Here  an  8-inch  layer  of  1-2-3  concrete  was  placed 
on  the  deck  and  allowed  to  harden  for  a  few  days  to  increase  the 
water- tightness  of  the  pockets.  The  caisson  was  then  gradu- 
ally built  up,  concrete  being  added  simultaneously  with  the 
building,  thus  causing  the  structure  to  sink.  At  the  start  the 
depth  of  water  was  about  50  feet  but  before  the  sinking  was 
completed  this  depth  had  increased  to  65  feet,  due  to  scour. 
The  caisson  was  guided  in  sinking  by  means  of  long  piles.  As 
soon  as  the  river  bottom  was  penetrated  a  few  feet,  the  concrete 
in  the  pockets  was  built  up  above  water-level  and  all  but  the 
2-inch  sheathing  was  omitted  around  the  wells.  The  material 
penetrated  was  mostly  sand  and  silt,  and  85  percent  of  this  was 
removed  by  the  sand- and  mud-pump  process  (Art.  91).  The 
caisson  finally  rested  on  a  bed  of  compact  gravel  135  feet  below 
the  normal  stage  of  the  river.  In  sinking,  the  water- jet 
was  used,  the  jet  pipes  being  in  the  positions  shown  in  the 
illustration. 


ART. 


CONSTRUCTION   WITH   TIMBER 


265 


Sec-Konal      Side      Eleva-Hon. 
Hatt      Top      Plan 


Sec-tional     End     Eleva-l-ion. 


Owtaide    Cutting    Edge.         Center  Cutting  Edge 
'       Horizon-tal     Section     A-B.  (Enlarged.) 

FIG.  88a. — Open  Caisson  for  Pier  IV,  Fraser  River  Bridge,  New  Westminster,  B.  C. 


266  BOX  AND   OPEN  CAISSONS  CHAP.  VII 

On  completion  of  the  sinking  concrete  was  deposited  in  the 
chamber  formed  by  the  flaring  out  of  the  wells  and  this  was  fol- 
lowed by  filling  the  wells.  This  concrete,  seventy  feet,  deep 
was  deposited  through  the  water  and  the  remainder  was  placed 
in  the  dry,  the  water  being  pumped  out  of  the  wells  previously 
to  placing  the  latter. 

The  caisson  for  Pier  3  of  this  bridge  when  well  down  in  the 
sand  encountered  sunken  logs,  causing  it  to  tilt.  One  of  these 
logs  had  a  diameter  of  2  feet  and  extended  clear  across  the  cais- 
son. This  was  removed  by  boring  holes  in  it  with  an  auger  100 
feet  long,  the  point  being  set  by  a  diver.  Into  these  holes  were 
placed  charges  of  dynamite  which  on  exploding  blew  the  log 
to  pieces.  The  top  of  the  caisson  was  surmounted  with  a  coffer- 
dam as  the  elevation  of  the  top  was  about  10  feet  below  ordinary 
water-level. 

Figs.  886  and  c  show  the  details  of  construction  for  the  36  X 
72-foot  open  caisson  of  the  Willamette  River  bridge,  of  the 
Oregon- Washington  Railroad  &  Navigation  Co.  There  were 
six  wells,  each  9X10  feet  in  the  clear,  flaring  out  at  the  bottom 
to  occupy  the  whole  area  of  the  caisson.  The  walls  of  the  wells 
and  the  outside  walls  of  the  caisson  were  made  of  a  single  thick- 
ness of  12 X  i2-inch  timbers  laid  close,  the  latter  being  sheathed 
on  the  outside  with  3-inch  material.  As  shown  in  the  plan  cer- 
tain timbers  of  the  well  walls  were  extended  the  entire  length 
and  breadth  of  the  caisson  to  brace  the  same. 

The  lower  part  of  the  caisson  consisted  of  V-shaped  walls  and 
bulkheads,  there  being  two  of  the  latter  running  transversely 
and  one  longitudinally.  The  widths  at  the  top  were  6  feet  for 
the  longitudinal  walls  and  bulkheads,  7  feet  for  the  transverse 
walls,  and  14  feet  for  the  longitudinal  bulkhead.  In  all  cases 
the  cutting  edges  were  reinforced  with  steel  angles  as  shown  in 
the  drawings. 

A  33-foot  cofferdam  surmounted  the  caisson,  the  walls  being 
of  the  same  construction  as  those  of  the  caisson,  except  that  the 
sheathing  consisted  of  i-inch  tongue-and-grooved  material,  with 
tar-paper  between  it  and  the  large  timbers.  The  cofferdam 
was  braced  with  horizontal  12X1 2-inch  timbers  running  both 


ART. 


CONSTRUCTION     WITH   TIMBER 


267 


:•     ^Concrete 


±f 1 

ir~""E 


i---- 

k 


d* 


i [ 


''•All  Rods  below  this  oneg'Diam. 


ft?l 


Section  E-  E .  Side  Elevation  (Sheathing Removed.) 

•  Sheathing  3  "Plank  -5-1-5  &2-E.,  3-7  "Spikes per sq.  ft 

72fr" 


Course  C. 


T- 


Course  B. 


Course 


Course 


Sectional 


Plan. 


FIG.  886. Open  Caisson  and  Cofferdam  for  the  Oregon- Washington  Railroad  and 

Navigation  Company's  Bridge  at  Portland,  Ore. 


268 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


longitudinally  and  transversely,  and  bearing  against  vertical 
12 X i2-inch  timbers,  which  in  turn  took  bearing  against  the 
walls  of  the  cofferdam. 

%l6r^±^^LMI°B°Lpier+tt-  *5 
fe^t.iE^5^  SJ^OKBry 

siT      ""'""•" 

&& 
#tyBfr-*fe 


Center  Transverse 
•Cutting   Edge. 
General  Notes: 

All  Timber 6-  4 -J  to uni-  ^"Drift- 

form  Dimensions.  EachT/'m-  Bolts 


C.  Alls" Drift  Bolts  Rivet  Head 


one  End  and  other Era /7/<7//z(-uttin3  Edge. 

All  other  Drift  Bolts  with  both 

Ends  plain.  p/a< 


be/ow 
g"D/am.        i-  j  t-i 

End  Elevation. 
Section  A-B.         (Sheathing  Removed) 


3" Rods  •,  !6"C.toC. 

Staggered-. 

-~6'o"~4-\ 


Section  F-F. 


End  Elevation. 
(Sheathing  Removed) 


Center  Longitudinal 
Cutting  Edge. 


Outside  Longitudinal 
Cutting  Edge. 


FIG.  88c. — Open  Caisson  with  Dredging  Wells  and  Superimposed  Cofferdam. 

Before  sinking  the  caisson,  borings  made  around  the  perimeter 
of  the  crib  showed  that  the  surface  of  the  good  bearing  stratum 
was  on  a  considerable  slope,  a  difference  of  22  feet  being  found 


ART.  88  CONSTRUCTION   WITH   TIMBER  269 

for  opposite  diagonal  corners.  To  level  this  off,  pipes  were  sunk 
and  holes  drilled  to  about  2  feet  below  the  lowest  elevation  of 
the  top  of  this  cemented  gravel  stratum.  Dynamite  was  placed 
in  these  holes  and  exploded,  and  in  this  way  the  hard  material 
was  broken  up  through  50  feet  of  gravel  and  sand,  before  any 
excavation  had  been  made.  When  the  caisson  reached  this 
cemented  gravel  the  latter  was  easily  removed  with  orange-peel 
buckets  working  through  the  dredging  wells.  The  depth  to 
which  the  caisson  was  sunk  was  about  130  feet  below  low  water, 
or  151  feet  below  high  water. 

The  Poughkeepsie  bridge,  which  spans  the  Hudson  River  at 
Poughkeepsie,  N.  Y.,  was  the  first  structure  in  America  to  be 
founded  on  deep  wooden  open  caissons,  and  to  date  (1914) 
these  caissons  are  the  largest  and  among  the  deepest  that  have 
ever  been  placed.  In  some  details,  such  as  filling  the  pockets 
with  gravel  instead  of  with  concrete,  and  using  a  removable 
cofferdam  on  grillage  on  top,  instead  of  the  ordinary  cofferdam, 
they  differ  materially  from  what  is  now  standard  practice. 

The  caisson  for  the  longest  pier  was  6oX  100  feet  in  plan  at 
the  bottom.  The  sides  were  vertical  for  a  height  of  40  feet 
from  the  bottom,  and  from  that  point  they  were  battered  to 
give  a  width  of  40  feet  at  the  top.  The  height  of  the  caisson 
was  104  feet,  and,  according  to  BAKER'S  Masonry  Construction, 
its  cutting  edge  rests  on  a  bed  of  gravel  134  feet  below  high 
water,  thus  making  the  top  of  the  caisson  23  feet  below  low 
water-level. 

Fourteen  dredging  wells,  10X12  feet  in  plan,  were  formed  by 
one  longitudinal  and  six  transverse  walls.  The  exterior  and 
longitudinal  walls  were  built  solid  and  of  a  triangular  section  for 
a  distance  of  20  feet  from  the  bottom;  at  this  point  the  thick- 
ness was  10  feet  for  the  side  walls,  9  feet  for  the  end  walls,  and 
1 6  feet  for  the  middle  longitudinal  wall.  Above  this  they  were 
hollow,  each  wall  dividing  into  two  2-foot  walls  with  a  hollow 
space  between,  the  latter  forming  the  filling  pockets.  The  six 
transverse  walls  were  made  2  feet  thick  and  extended  from  the 
cutting  edge  to  the  top  of  the  caisson.  All  walls  were  made  of 
12 X i2-inch  material  laid  horizontally. 


270  BOX  AND   OPEN   CAISSONS  CHAP.  VII 

The  sinking  was  accomplished  by  dredging  through  the  wells 
with  a  clam-shell  bucket  and  by  filling  the  pockets  with  gravel. 
Care  had  to  be  taken  that  the  pockets  were  completely  filled 
before  the  top  of  the  caisson  reached  water-level,  in  order  that  a 
layer  of  i2Xi2-inch  timber  could  be  laid  over  these  pockets. 
The  remainder  of  the  dredging  was  done  with  the  top  of  the 
wells  submerged.  On  the  caisson  reaching  the  desired  depth 
the  wells  were  filled  with  concrete. 

A  grillage  6  feet  thick  was  then  constructed  and  temporary 
walls  6  feet  high  were  built  on  it.  This  was  floated  to  position 
over  the  caisson  and  masonry  built  up  in  it.  As  soon  as  the 
weight  of  the  masonry  was  sufficient  to  cause  the  walls  to  become 
submerged,  the  latter  were  removed,  the  masonry  by  this  time 
being  well  above  the  surface  of  the  water.  More  masonry  was 
added  until  the  grillage  came  to  a  bearing  on  the  caisson,  after 
which  the  remainder  of  the  masonry  pier  was  built. 

ART.  89.     CONSTRUCTION  WITH  METAL 

The  use  of  iron  and  steel  shells  for  open  caissons  of  other  than 
the  cylindrical  form  has  not  found  favor  in  America;  on  the 
other  hand,  English  engineers  have  made  extensive  use  of  this 
type.  A  general  statement  may  perhaps  be  made  that  where 
the  American  engineer  will  use  a  pneumatic  caisson  of  wood  his 
English  brother  will  use  an  open  caisson  of  metal,  either  steel, 
wrought  iron,  or  cast  iron. 

The  two  advantages  possessed  by  this  type  of  caisson  are: 
First,  the  speed  with  which  the  caisson  may  be  built;  and 
second,  the  small  space  occupied  by  the  metal,  thus  leaving  a 
maximum  amount  of  space  for  the  concrete  filling.  The  dis- 
advantages are:  First,  the  cost  of  the  caisson,  especially  where 
the  metal  has  to  be  transported  long  distances;  and  second,  the 
lack  of  permanency  of  the  metal. 

One  of  the  most  notable  examples  of  the  use  of  open  caissons 
with  dredging  wells  in  bridge  foundations  is  that  of  the  sub- 
structure of  the  Hawkesbury  bridge  in  southwestern  Australia, 
where  the  caissons  were  sunk  to  a  maximum  depth  of  almost  162 


ART.  89  CONSTRUCTION   WITH   METAL  271 

feet  below  high  water,  the  range  of  tide  being  7  feet.  This 
depth  gives,  that  bridge  the  deepest  foundations  which  have  ever 
been  used,  although  in  the  proposed  (1902)  new  Sidney  Harbor 
bridge  it  is  stated  that  the  open  caissons  will  be  sunk  to  a  depth 
of  170  feet  below  water-level. 

The  caissons  of  the  Hawkesbury  bridge  were  oblong  in  plan 
with  rounded  ends,  the  length  being  48  feet  and  the  width  20 
feet.  The  lower  20  feet  is  splayed  out  to  form  a  tapered  shoe  2 
feet  wider  all  around  the  bottom.  Along  the  center  line,  paral- 
lel with  its  length  were  three  wrought-iron  dredging  tubes,  8 
feet  in  diameter  and  14  feet  apart  on  centers,  strongly  braced  to 
the  sides  of  the  caisson  and  to  each  other.  At  the  bottom  these 
wells  splayed  out  in  the  form  of  a  trumpet  mouth  to  meet  the 
outer  skin  and  each  other  in  a  cutting  edge  made  of  steel. 
Between  these  wells  and  the  sides  of  the  caisson  were  pockets 
to  be  filled  with  concrete  as  the  caisson  sank. 

Sections  of  steel  for  the  sides  and  of  wrought  iron  for  the 
dredging  tubes  were  added  as  the  caisson  sank,  the  sinking  being 
effected  by  dredging  out  the  material  under  the  caisson  through 
the  wells  and  by  filling  the  pockets  with  concrete.  All  caissons 
were  bedded  on  firm  sand  which  was  overlaid  with  mud  and  silt 
of  varying  depth,  that  at  Pier  6  being  108  feet  with  a  depth  of 
water  at  low  tide  of  47  feet.  As  soon  as  the  caissons  were 
firmly  bedded  in  the  sand,  the  wells  were  filled  with  concrete 
and  the  pier  masonry  was  started  at  a  depth  somewhat  below 
low  water. 

The  experience  gained  in  sinking  these  caissons  showed  that 
it  is  not  advisable  to  splay  out  the  outside  walls  of  a 
caisson.  If  this  is  done  the  guiding  effect  of  the  surrounding 
material  is  largely  lost,  and  a  very  troublesome  condition 
obtains  when  on  one  side  the  earth  is  firmer  than  on  the  other, 
thus  standing  for  some  time  after  the  other  has  fallen  in,  as  a 
consequence  of  which  the  caisson  is  forced  out  of  position. 

In  the  construction  of  the  Dufferin  bridge  piers  over  the 
Ganges  River  at  Benares,  the  caissons,  which  were  elliptical  in 
form  and  65  X  29  feet  in  plan,  had  their  pockets  filled  with 
brickwork,  only  the  lower  6  feet  being  of  concrete.  In  the 


272  BOX  AND   OPEN  CAISSONS  CHAP.  VII 

Hooghly  bridge  caissons  the  outer  skin  was  vertical  all  the  way 
from  the  bottom,  while  the  three  dredging  chambers  extended 
across  the  structure  and  occupied  the  two  semi-circular  ends  as 
well  as  the  central  portion,  the  remainder  forming  two  pockets 
each  15  feet  in  width.  Sinking  weight  was  obtained  by  con- 
creting the  two  pockets  and  by  a  brick  lining,  3  feet  wide,  around 
the  semi-circular  ends,  this  lining  resting  on  horizontal  shelf 
angles  spaced  4  feet  apart  vertically.  The  upper  part  of  the 
central  well  also  had  a  brick  lining. 

ART.  90.     CONSTRUCTION  WITH  CONCRETE 

The  use  of  concrete  open  caissons,  usually  reinforced,  is 
rapidly  increasing,  and  without  doubt  this  type  will  replace  the 
other  forms  in  the  future.  The  concrete  type  offers  many 
advantages  over  those  made  of  wood  or  metal:  it  does  away 
with  the  uncertainty  of  future  decay  or  corrosion;  its  greater 
specific  gravity,  compared  with  wood,  makes  less  weighting 
necessary  in  sinking  than  when  the  wooden  type  is  used;  its 
cost  will  compare  favorably  with  the  other  forms;  and  lastly, 
with  its  concrete  filling  it  forms  a  monolithic  foundation,  far 
stronger  and  better  than  any  combination  structure.  All  cais- 
sons, whether  of  wood,  steel,  or  concrete,  furnish  essentially  a 
concrete  foundation  for  the  pier,  the  shell  being  the  only  part 
which  may  not  be  of  concrete.  The  one  possible  disadvantage 
of  the  concrete  caisson  is  the  greater  time  element  involved, 
since  the  shell  cannot  be  sunk  until  it  has  hardened  for  some 
time,  but  if  the  work  is  properly  laid  out  this  element  will 
be  of  little  moment.  , 

One  of  the  piers  of  the  American  River  bridge,  of  the  Southern 
Pacific  Railroad,  was  founded  upon  a  concrete  open  caisson,  the 
details  of  which  are  shown  in  Fig.  900,  while  Fig.  god  shows  the 
forms  used  for  this  caisson.  The  physical  conditions  at  the  site 
were  peculiar.  The  hard-pan,  which  was  covered  by  a  bed  of 
cobblestones  and  small  boulders  was  from  40  to  60  feet  below 
water-level.  When  the  water  was  low  a  deposit  of  fine  gravel 
and  silt  overlaid  the  cobbles,  but  when  freshets  came  this  gravel 


ART. 

Watert 

go 

CONSTRUCTION    WITH 

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FIG.  9oa.— Open  Caisson  and  Cofferdam  for  Pier  2  of  Southern  Pacific  Railroad 

Bridge  over  American  River  near  Elvas,  Cal. 
18 


274  BOX  AND   OPEN   CAISSONS  CHAP.  VII 

and  silt  were  entirely  scoured  out.  The  reinforced-concrete 
caisson  used  for  Pier  2  was  28X76  feet  in  plan  and  22  feet  in 
height.  The  side  and  end  walls  were  3  feet  thick,  while  the 
three  cross  walls  which  divided  the  structure  into  four  compart- 
ments, were  each  4  feet  thick.  The  cutting  edges  were  made  by 
beveling  the  walls,  and  each  of  these  cutting  edges  was  rein- 
forced with  angles  and  plates.  The  walls  were  reinforced  near 
the  bottom  with  old  steel  rails  laid  horizontally. 

The  caisson  was  sunk  during  a  time  when  the  bed  of  the 
stream  was  dry,  the  soil  being  first  excavated  down  to  ground 
water-level,  after  which  the  forms  were  placed  and  the  concrete 
poured,  the  entire  caisson  being  built  before  any  sinking  was 
done.  Sinking  was  effected  by  excavating  the  material  from 
the  compartments  with  an  orange-peel  bucket.  When  down  to 
about  ground  level  a  cofferdam  was  added.  When  the  cutting 
edge  reached  the  stratum  of  cobbles  and  boulders,  sinking  opera- 
tions were  stopped  and  the  compartments  of  the  caisson  were 
filled  with  concrete,  after  which  the  pier  was  built  in  the  coffer- 
dam. The  process  of  sinking  was  slow  owing  to  the  fact  that  no 
weighting  was  done. 

laThe  concrete  caisson  was  surmounted  by  a  timber  coffer- 
dam, 28  feet  high,  which  had  tiers  of  horizontal  rangers  and 
braces  attached  to  loXio-inch  uprights  anchored  to  the  con- 
crete. The  lower  courses  of  rangers  were  also  anchored  to  the 
latter,  a  special  joint  being  formed  between  them  and  the  top 
of  the  walls  to  prevent  leakage  at  this  point.  The  sides  of  the 
timber  cofferdam  were  formed  by  two  courses  of  i^-inch 
ship-lap  nailed  closely  to  the  rangers.  The  inside  walls  of  each 
compartment  were  also  sheathed  with  3  X  8-inch  vertical  pieces, 
spaced  8  inches  apart." 

One  of  the  most  notable  examples  of  the  use  of  the  all-concrete 
open  caisson  is  that  for  the  Beaver  bridge  of  the  Pittsburgh  & 
Lake  Erie  Railroad.  They  were  among  the  first  of  the  all- 
concrete  caissons,  being  placed  in  1908,  and  the  largest  to  that 
date.  Two  novel  features  were:  First,  the  very  considerable 
thickness  of  walls,  making  it  possible  to  dispense  with  reinforce- 

1  Engineering  Record,  vol.  62,  page  232,  Aug.  27,  1910. 


ART.  90 


CONSTRUCTION    WITH   CONCRETE 


275 


ment  in  the  concrete;  and  second,  the  use  of  the  pneumatic  proc- 
ess in  bedding  the  caissons.  The  pneumatic  feature  of  these 
caissons  is  described  in  Art.  99. 

At  the  site  of  the  piers  the  ordinary  depth  of  water  was  about 
7  feet,  with  bedrock  about  38  feet  below  the  bed  of  the  river. 
The  overlying  material  was  mostly  sand  and  gravel,  with  many 
boulders  scattered  throughout  the  mass. 


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FIG.  906. — Caisson  for  P.  &  L.  E.  R.  R.  Bridge,  Beaver,  Pa. 

The  caissons,  views  of  which  are  shown  in  Figs,  gob  and  c, 
consisted  of  a  concrete  shell  7  feet  thick,  this  thickness  being 
maintained  from  the  top  to  a  point  about  9  feet  above  the  shoe, 
at  which  elevation  it  tapered  to  an  8-inch  cutting  edge.  This 
cutting  edge  or  shoe  was  formed  by  an  8X8 Xf -inch  angle 
and  a  2iX|-inch  bent  plate,  the  vertical  leg  of  the  angle  extend- 
ing upward  on  the  outer  face  of  the  caisson,  while  the  bent  plate 
had  its  inclined  leg  along  the  inner  face  of  the  wall.  Rods 
|  inch  in  diameter  and  10  feet  long,  extending  up  into  the 
concrete,  held  the  shoe  in  place.  There  were  two  cross  walls 
each  5  feet  thick  to  stiffen  the  caisson,  and  these  extended 
from  the  top  of  the  caisson  to  about  3  feet  above  the  shoe,  a 


276  BOX  AND   OPEN  CAISSONS  CHAP.  VII 

trapezoidal  portion  at  the  bottom  of  each  wall  about  6  feet  in 
height,  being  omitted. 

Rectangular  cofferdams  were  first  constructed  around  the 
site  of  each  pier  and  these  were  unwatered  to  permit  building 
the  forms  for  the  caissons.  On  completion  of  the  forms  a  six- 
foot  depth  of  concrete  was  deposited  in  the  same  and  allowed  to 
harden  before  more  was  added. 

Sinking  was  accomplished  for  the  most  part  by  dredging 
through  the  three  wells  with  orange-peel  buckets.  When  it 
was  possible  to  keep  the  water  down  by  pumping,  the  spoil 
under  the  shoe  of  the  caisson  was  removed  by  hand  to  within 
reach  of  the  buckets.  Later,  when  boulders  were  encountered 
under  the  cutting  edge  they  were  removed  by  divers.  When 
the  caisson  showed  a  tendency  to  stick,  the  water-jet  was  used. 
When  within  about  16  inches  of  the  rock  the  pneumatic  process 
was  brought  into  use  as  explained  in  Art.  99. 

That  the  omission  of  reinforcement  in  a  structure  like  the  one 
just  described  may  prove  a  costly  mistake  was  shown  in  the  cais- 
sons for  the  North  Side  Point  bridge,  across  the  Allegheny 
River,  Pittsburgh,  Pa.  The  caisson  for  the  river  pier  had 
dimensions  of  23  X  83!  feet  in  plan,  with  four  rectangular  wells, 
9X10  feet,  and  spaced  19  feet  center  to  center.  When  the 
pier  had  been  sunk  to  a  depth  of  17  feet  below  river  bottom,  a 
transverse  crack  developed  at  about  mid-length  and  extended 
from  the  top  to  the  river  bottom  as  shown  at  the  left  in  Fig. 
goe.  The  cracking  was  due  to  the  unequal  dredging  in  the 
different  wells,  causing  the  weight  of  the  caisson  to  bear  chiefly 
at  mid-length.  The  cracked  caisson  was  blasted  to  pieces  and 
rernoved.  The  one  placed  afterward  had  smaller  wells,  and  was 
reinforced  with  longitudinal  rods. 

For  an  example  of  caissons  for  buildings  which  are  sunk  as 
open  caissons  and  can  be  transformed  into  the  pneumatic 
type  see  Engineering  Record,  vol.  63,  page  185,  Feb.  18, 
1911. 

The  first  all-concrete  open  caisson  used  for  bridge  foundations 
in  this  country  is  probably  the  one  for  pier  D  of  the  Thebes 
Cantilever  bridge.  This  caisson  is  19X38  feet  in  plan  and 


II 


ll 

rlf* 


FIG.  god. — Forms  for  Open  Caisson  of  Concrete.     See  Fig. 


FIG.  Qoe. — Cracks  in  Caisson  of  Concrete  without  Reinforcement. 


ART.  91  SINKING   OPEN   CAISSONS  277 

was  placed  in  the  winter  of  1902-03.  An  open  caisson  (which 
was  not  constructed  of  either  timber  or  metal)  was  first  sunk  in 
this  country  in  1898  by  the  Dravo  Contracting  Co.,  at  Neville 
Island  near  Pittsburgh  and  was  used  for  a  pump  well. 

ART.  91.     SINKING  OPEN  CAISSONS 

There  are  five  methods  used  in  sinking  open  caissons:  First, 
removing  the  material  from  within  the  caisson;  second,  weight- 
ing the  structure;  third,  using  the  water-jet;  fourth,  driving 
down  the  caisson;  and  fifth,  pulling  down  the  caisson. 

The  first  method,  which  represents  the  fundamental  idea  of 
the  open  caisson,  is  always  employed.  For  the  small  caisson,  to 
be  sunk  but  a  few  feet,  as  practised  by  the  natives  of  countries 
in  the  Far  East,  excavating  is  done  by  baskets  carried  down, 
filled  and  brought  up  by  divers.  The  modern  method  consists 
in  pumping,  or  in  dredging  out  the  material  with  buckets. 

The  mud  and  sand  pump,  the  principle  of  which  is  described 
in  Art.  107,  is  used  where  the  material  is  largely  silt,  or  other  soft 
material.  Fig.  gia  illustrates  the  pump  used  on  the  Fraser 
River  bridge,  at  New  Westminster,  British  Columbia.  This 
pump,  or  ejector,  which  was  operated  by  a  hydraulic  jet,  at  a 
pressure  of  125  pounds  per  square  inch,  could  handle  anything 
with  a  diameter  of  less  than  3  inches.  The  dimensions  of  the 
pump  are  shown  in  the  illustrations.  The  top  of  the  pressure 
pipe  was  fitted  with  a  ball-and-socket  joint  and  a  9o-degree 
bend  with  an  enlarger  to  which  were  connected  three  lines  of  2\- 
inch  fire  hose.  A  separate  hydraulic  jet,  having  a  f-inch  hole 
at  the  bottom  and  five  f-inch  holes  in  nearly  vertical  planes  on 
the  circumference  of  a  circle  and  a  few  inches  above  the  bottom, 
was  used  to  agitate  the  material  around  the  intake  of  the  ejector. 

The  most  common  method  of  removing  material  is  by  dredg- 
ing with  an  orange-peel  or  a  clam-shell  bucket.  Where  a  layer 
of  stiff  clay  is  met  it  may  be  broken  up  by  sending  divers  down 
to  blast  it  to  pieces,  or  it  may  sometimes  be  broken  up  by 
dropping  down  long  steel  rails  vertically,  which  sink  into  the 
clay  and  tear  it  up  in  tipping  over.  A  line  is  attached  to  the 
rails  to  withdraw  them. 


278 


BOX   AND   OPEN   CAISSONS 


CHAP.  VII 


The  most  economical  way  to  weight  caissons  is  by  making  use 
of  the  permanent  filling,  and  for  this  reason,  where  the  size  of  the 
caisson  makes  it  possible,  a  double  wall  should  always  be  used. 
Temporary  weighting,  as  with  rails  laid  on  top,  etc.,  is  always 
expensive  on  account  of  the  time  and  labor  involved,  as  well  as 
on  account  of  obstruction  to  the  dredging  operations. 


FIG.  gia. — Details  of  Hydraulic  Ejector. 


FIG.  916. — Tip 
of  Water  Jet. 


The  rapid  and  successful  sinking  of  the  Hawkesbury  bridge 
caissons  (Art.  89)  was  largely  due  to  their  being  designed  to  carry 
a  large  mass  of  concrete  between  the  outer  and  inner  shells, 
which  was  placed  during  sinking. 

The  water-jet  (Art.  17)  is  always  a  useful  adjunct  in  caisson- 
sinking  operations.  By  using  the  same  freely  around  the  cut- 


ART.  91  SINKING   OPEN   CAISSONS  279 

ting  edges  and  along  the  sides  the  frictional  resistance  is  con- 
siderably decreased.  Another  advantage  is  that  it  tends  to 
wash  the  material  toward  the  interior  of  the  caisson,  where  it 
can  be  picked  up  by  the  dredging  buckets,  which  have  previ- 
ously made  a  hole  in  the  center. 

It  is  possible  to  drive  caissons  only  when  they  are  small  and 
even  then  only  light  blows  with  the  hammer  may  safely  be  given. 
Pulling  the  caisson  down  may  sometimes  be  employed  to  advan- 
tage, if  it  is  possible  to  drive  piles  around  the  outside  and  attach 
tackle  to  them  and  to  the  sides  of  the  caisson. 


CHAPTER  VIII 
PNEUMATIC  CAISSONS  FOR  BRIDGES 

ART.  92.    THE  PNEUMATIC  PROCESS 

The  use  of  the  plenum  pneumatic  process  for  founding  deep 
piers  is  a  good  example  of  the  application  of  scientific  principles 
to  foundation  work.  A  pneumatic  caisson  may  be  defined  as  a 
structure,  open  at  the  bottom  and  closed  at  the  top — in  other 
words,  an  inverted  box — in  which  compressed  air  is  utilized  to 
keep  the  water  and  mud  from  coming  into  the  box,  and  which 
forms  an  integral  part  of  the  foundation. 

The  caisson,  which  is  usually  not  over  6  feet  high  in  the  work- 
ing chamber,  is»surmounted  by  a  crib  and  cofferdam,  the  former, 
with  the  exception  of  one  or  more  vertical  wells,  called  shafts, 
being  filled  with  concrete  as  the  caisson  sinks.  This  concreting, 
together  with  the  excavating  done  in  the  working  chamber, 
as  the  interior  of  the  caisson  is  called,  effects  the  sinking 
of  the  latter. 

The  working  chamber  must  be  practically  air-  and  water- 
tight, and  yet  there  must  be  an  opening  for  men  to  enter  and 
leave  the  chamber,  as  well  as  an  inlet  and  outlet  for  materials. 
These  openings  are  provided  by  vertical  shafts  and  air-locks. 
The  shafts,  wjiich  extend  from  the  roof  of  the  caisson  to  a 
point  well  above  the  top  of  the  crib  and  the  level  of  the  water 
outside,  are  usually  of  a  circular  or  oval  section  and  from  i\  to 
4  feet  in  maximum  diameter.  In  the  shafts,  at  the  bottom, 
top,  or  between  these  two  points,  are  placed  the  air-locks,  they 
being  air-tight  chambers,  often  simply  a  part  of  the  shaft  itself, 
fitted  with  two  doors,  one  of  which  leads  to  the  working  chamber 
and  the  other  to  the  open  air. 

The  most  pronounced  advantage  of  the  pneumatic  caisson  as 
compared  with  the  open-caisson  process  lies  in  the  fact  that  the 

280 


ART.  92  THE   PNEUMATIC   PROCESS  281 

engineer  has  more  control  over  the  work,  having  a  better  oppor- 
tunity to  sink  the  caisson  vertically,  to  remove  large  boulders, 
sunken  logs,  etc.,  from  under  the  cutting  edge;  the  foundation 
bed  can  be  properly  prepared  and  personally  inspected;  and 
lastly,  the  concrete  filling  of  the  working  chamber  is  deposited  in 
air,  thus  giving  a  superior  foundation"  Another  point,  which  is 
sometimes  of  great  importance  in  placing  foundations  for  build- 
ings, is  that  the  soil  about  the  caisson  is  not  so  liable  to  be  dis- 
turbed when  the  pneumatic  process  is  used.  The  one  disadvan- 
tage of  this  process  is  that  the  men  have  to  work  under  an  air 
pressure  which  is  sufficient  to  balance  the  pressure  of  the  sur- 
rounding water  in  addition  to  atmospheric  pressure,  or  practi- 
cally the  full  hydrostatic  head  from  the  cutting  edge  to  the 
water  surface. 

For  depths  from  about  30  to  no  feet  this  type  of  caisson  is 
extensively  employed.  For  depths  less  than  30  feet  the  coffer- 
dam process  is  usually,  but  not  always,  a  more  economical 
method  of  placing  the  foundation  while  for  depths  greater  than 
about  no  feet,  corresponding  to  a  pressure  of  over  three 
atmospheres  above  the  normal,  the  open-caisson  method  must 
be  employed,  since  men  cannot  work  advantageously  under 
such  high  pressures. 

At  the  St.  Louis  Municipal  bridge  men  worked  at  a  maximum 
immersion  of  over  113  feet,  the  maximum  gage  pressure  being 
50  pounds,  which  is  probably  the  world  record  for  bridge 
caissons,  with  the  possible  exception  of  a  bridge  caisson  in 
Denmark,  where  it  is  reported  (Eng.  News,  vol.  26,  page 
467,  Nov.  14,  1891)  that  a  working  depth  of  115  feet  was 
reached.  Among  other  notable  examples  of  deep  immersions 
are  the  St.  Louis  arch  bridge  caissons,  109.7  feet;  the  Memphis 
bridge  caissons,  106.4  feet;  the  Williamsburg  bridge  (New 
York)  caissons,  107.5;  and  the  Broadway  bridge  (Portland, 
Ore.)  caissons,  101  feet.  The  elevation  of  the  bottom  of 
the  deepest  caisson  (No.  4)  of  the  St.  Louis  Municipal  bridge 
is  2.1  feet  below  the  bottom  of  the  east  abutment  caisson,  or 
the  deepest  one  of  the  St.  Louis  arch  bridge. 

The  caisson  used  in  sinking  a  mine  shaft  near  Deerwood, 


282  PNUEMATIC   CAISSONS   FOR  BRIDGES  CHAP.  VIII 

Minn.,  was  sunk  to  a  depth  of  123  feet  below  ground- water 
level  and  130  feet  below  the  ground  surface.  The  maximum 
pressure  used  was  52  pounds  per  square  inch,  a  higher  value 
than  has  probably  ever  been  used  in  bridge  or  building  caissons. 

As  first  applied  the  pneumatic 'caisson  process  was  a  very 
simple  affair,  the  caisson  Consisting  of  a  cast-iron  cylinder,  called 
a  pneumatic  pile,  which  formed  both  the  working  chamber  and 
a  section  of  the  pier.  The  first  used  in  this  country  were  sunk 
in  1852  in  the  Pedee  River,  North  Carolina. 

The  St.  Louis  arch  bridge  was  the  first  in  this  country  to  be 
founded  on  large  pneumatic  caissons,  its  east  abutment  caisson, 
which  had  a  maximum  immersion  of  109  feet  8|  inches,  being 
sunk  in  1870.  The  second  bridge  in  this  country  to  be  founded 
on  large  pneumatic  caissons  was  the  great  Brooklyn  suspension 
bridge,  which,  in  its  New  York  tower  caisson,  sunk  in  1871, 
has  the  largest  pneumatic  caisson  ever  placed  for  a  bridge 
foundation.  It  was  102  by  172  feet  in  plan  and  was  sunk  to  a 
depth  of  78  feet  below  high-water  level. 

The  pneumatic  caisson  process  has  been  widely  used  in 
America  and  on  the  European  continent.  As  a  class,  English 
engineers  have  apparently  shown  some  aversion  to  it,  and  in 
many  cases,  where  it  seems  to  have  been  the  preferable  struc- 
ture on  account  of  the  presence  of  boulders  and  logs,  the  open- 
caisson  process  was  used.  American  engineers  have  developed 
the  wooden  caisson  to  a  high  state  of  perfection,  but  at  present 
(1914)  owing  to  the  high  price  of  timber  the  tendency  is 
toward  the  use  of  more  .reinforced  concrete  and  less  timber. 
In  Europe  the  metallic  form  of  pneumatic  caisson  has  been 
extensively  used. 

To  give  some  indication  of  the  progress  made  in  the  science 
and  art  of  foundation  construction  it  is  interesting  to  note  that 
the  cost  per  cubic  yard  of  the  substructure  of  the  Municipal 
bridge  at  St.  Louis  is  only  29.6  percent  of  the  corresponding 
cost  of  that  of  the  St.  Louis  arch  bridge,  which  is  located  about 
a  mile  above  it,  and  50.8  percent  of  that  of  the  Memphis  bridge. 
The  substructures  of  these  three  bridges  were  completed  in 
1911,  1871  and  1891  respectively.  In  this  comparison  the 


ART.  93  CAISSON  ROOF   CONSTRUCTION  283 

approaches    are    excluded.     As    previously    noted,     the  three 
bridges  have  deep  foundations. 

The  contract  price  for  the  caisson  work  of  the  Municipal 
bridge  was  $27.00  per  cubic  yard  below  the  cutting  edge,  and 
$12.90  per  cubic  yard  from  the  cutting  edge  to  the  top  of  the 
crib. 

ART.  93.     CAISSON  ROOF  CONSTRUCTION 

TIMBER  ROOFS. — The  design  of  the  roof  has  always  been 
largely  a  question  of  judgment  as  it  is  almost  impossible  to 
analyze  the  stresses.  The  tendency  of  roof  construction  has 
been  constantly  to  decrease  the  thickness  of  the  timber  roof 
and  consequently  its  cost.  When  concrete  superseded  stone 
masonry  as  a  filling  for  the  crib  a  considerable  decrease  in 
the  thickness  of  the  roof  was  made  possible  on  account  of  the 
strength  of  the  concrete.  A  more  generous  use  of  bulkheads 
and  the  arrangement  of  the  bracing  above  and  below  the  deck 
to  act  as  trusses  also  aided  in  securing  a  thinner  roof.  At 
present  many  caissons  do  away  with  a  permanent  timber  roof 
almost  entirely  by  reinforcing  the  concrete  filling  of  the  crib. 

The  roof  is  usually  made  with  layers  of  i2Xi2-inch  timbers, 
sheathed  on  the  lower  side  with  2-  or  3-inch  planks.  Sheathing 
may  also  be  used  between  the  courses  of  large  timbers.  The 
different  courses  run  in  different  directions;  if  the  roof  is  of 
a  two-course  thickness  both  courses  may  run  transversely, 
while  if  it  has  three  courses  the  lower  and  upper  courses  run 
transversely  and  the  middle  course  longitudinally.  All  caulk- 
ing of  the  air  chamber  is  done  from  the  inside  of  the  work- 
ing chamber,  against  the  air  blowing  out,  while  the  outside 
planking  is  caulked  from  the  outside,  to  prevent  the  water  from 
getting  in. 

The  roof  of  the  io2Xi72-foot  caisson  for  the  New  York 
tower  of  the  Brooklyn  bridge  was  composed  of  a  solid  mass  of 
squared  timbers,  22  feet  thick,  all  timbers  being  12X12  inches 
in  section,  and  thoroughly  drift-bolted  together.  This  is  the 
thickest  roof  that  has  ever  been  used. 


284 


PNEUMATIC    CAISSONS   FOR   BRIDGES 


CHAP.  VIII 


The  roof  of  the  31X79- 
foot  rectangular  caisson  for 
the  old  piers  of  the  Baltimore 
and  Ohio  Railroad  bridge  at 
Havre  de  Grace  was  composed 
of  eight  thicknesses  of  1 2  X 1 2- 
inch  timbers,  the  courses 
alternating  in  direction,  some 
running  longitudinally,  others 
transversely,  and  still  others 
diagonally.  The  lower  sur- 
face was  sheathed  with  3X 
i2-inch  planks.  This  form 
of  roof  is  typical  of  a  num- 
ber of  caissons  built  under 
the  direction  of  WILLIAM 
PATTON,  who  was  an  extrem- 
ist in  respect  to  thick  roofs. 

The  roof  of  the  east  abut- 
ment  caisson  of  the  St.  Louis 
arch  bridge  was  only  4  feet 
10  inches  thick,  the  upper 
three  layers  being  composed 
of  i6Xi6-inch  timbers.  The 
shape  of  this  caisson  was  an 
irregular  hexagon,  with  ex- 
treme dimensions  of  82  by 
7  2^  feet.  This  comparatively 
thin  roof  was  made  possible 
by  the  use  of  two  wooden 
bulkheads  below  the  roof  and 
two  iron  girders  above,  the 
latter  running  at  right 
angles  to  the  former,  and 
all  supporting  the  roof.  The 
upper  surface  of  this  roof 
was  covered  with  plate  iron, 


ART,  93 


CAISSON  ROOF   CONSTRUCTION 


285 


286 


PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  VIII 


ART.  93 


CAISSON   ROOF   CONSTRUCTION 


287 


while  in  the  Brooklyn  bridge  caissons  the  under  side  was  cov- 
ered with  wr ought-iron  plates;  in  both  cases  this  was  done  to 
obtain  an  air-tight  roof.  It  was  a  very  expensive  method, 
since  oakum  caulking  is  sufficient.  But  in  the  Brooklyn  bridge 
caissons  it  was  done  for  the  added  purpose  of  fire  protection,  for 


*f°g  VW.K- v_v  *2ro,www,#'is 


288 


PNEUMATIC   CAISSONS   FOR  BRIDGES 


CHAP.  VIII 


in  those  early  caissons  torches  were  used  for  lighting  purposes, 
and  as  there  was  always  a  considerable  amount  of  air  escaping 
between  the  timbers  the  danger  of  fire  was  very  great. 


ection  at  Tbp  of  Caisson 
Supply  5 ha  ft, 

v 


Note ;  All  Posts  marked  S3  enctat'Top  of  the  Courses  in  whichtheyareshown 

Sectional          Plqn. 
FIG.   93<?. — Pneumatic  Caisson  for  Broadway  Bridge,  Portland,  Ore. 


ART.  93 


CAISSON  ROOF   CONSTRUCTION 


289 


In  recent  years  the  tendency  has  been  to  use  more  courses  of 
3-inch  sheathing,  usually  tongue  and  groove,  in  order  to  get 
a  more  nearly  air-tight  roof.  As  shown  in  Fig.  930  the  roof  of 


FIG. 


Showing    Inner 

Face  of  Wall 
and  Kneebraces 


Showing  Braces 

and 
Bulkhead 


Section  A  "A 
FIG.  93<;.  —  Quebec  Bridge  Caisson. 


8" Drift 

Bol1--'\w^r.       -..-, 

Channel 
FIG.  93/1. — Section  of  Cutting  Edge. 


j'fffiote 


Joint 


k  p. 

•M-  **  «.*"^  •'  •    •""•!"            —        H55ysil         H_ 

& 

| 

^     I 

5  I 

p: 

\               *Jo/f7f                                                7  "Channel          / 

h 

V      t£a 

FIG.  93^. — Plan  of  Steel  Cutting -Edge.     Broadway  Bridge. 


290 


PNEUMATIC    CAISSONS   FOR  BRIDGES 


CHAP.  VIII 


ART.  93 


CAISSON  ROOF   CONSTRUCTION 


291 


the  caisson  for  pier  4  of  the  Bellefontaine  bridge,  built  in  1892, 
consisted  of  two  courses  of  large-size  timbers,  between  which 
were  placed  two  courses  of  sheathing,  laid  diagonally.  The 
lower  side  of  the  roof  was  also  lined  with  sheathing.  Another 


FIG.  93;. — Half  Longitudinal  and  Half  Transverse  Sections. 

notable  feature  of  this  roof, 
which  is  characteristic  of 
many  built  by  Geo.  S. 
MORISON,  is  the  relatively 
thin  roof  used.  This  was 
made  possible  by  connec- 
ting the  roof  to  the  bracing 
timbers  of  the  crib  above 
by  means  of  tie  rods. 

As  shown  in  Figs.  936,  c, 
and  d  the  roof  of  the  south 
main  pier  caisson  of  the 
new  Quebec  bridge  con- 
sisted of  one  solid  course 
of  longitudinal  and  one 
solid  course  of  transverse 

timbers,  Separated  by  tWO  FIG.  93^.— Framing  of  Cofferdam. 

crossed  courses  of  diagonal 

3-inch  tongue-and-grooved  planks.     Here  numerous  bulkheads 

made  possible  a  thin  roof. 


Half   End    Elevation 


Half  Secti'on 


PNEUMATIC   CAISSONS   FOR  BRIDGES 


CHAP.  VIII 


la 


§    If 

o    ^  5 


fill 

n   g   g   W> 


So 
g 

o 

"§ 
I 


*C  H     _.  ^-i 


B«sll 

B  w   3 


O        gg 

S     ^£ 


>-i    O 

ll 


a.*|j 

§  rt  S? 


ART.  94  SIDES   OF   WORKING   CHAMBER  293 

example  of  a  reinforced-concrete  roof  is  that  for  the  caissons 
of  the  Passyunk  Ave.  highway  bridge  piers,  across  the 
Schuylkill  River,  Philadelphia.  The  largest  caisson  was  22X60 
feet  in  plan  and  its  roof  was  reinforced  with  i-inch  square, 
twisted  horizontal  rods  running  transversely  and  spaced  12 
inches  on  centers.  The  thickness  of  the  concrete  slab  first 
cast  was  18  inches,  the  forms  consisting  of  a  temporary 
wooden  ceiling  of  3  X 1 2-inch  planks. 

ART.  94.     SIDES  OF  WORKING  CHAMBER 

The  sides  of  the  caisson  should  be  made  strong  and  rigid 
enough,  not  only  to  take  the  direct  vertical  loads,  but  also  to 
withstand  safely  sudden  lateral  thrusts,  eccentric  loads  due  to 
unequal  sinking  of  opposite  sides,  etc.  To  prevent  leakage  of 
air  outward  and  of  water  inward  all  joints  should  be  thoroughly 
caulked.  The  necessary  thickness  of  walls  will  depend  some- 
what on  the  clear  height  of  the  working  chamber,  as  well  as  on 
the  kind  of  material  through  which  the  caisson  is  to  be  sunk. 
The  clear  height  should  not,  however,  vary  much  from  6  feet. 

The  sides  must  be  vertical.  To  batter  the  sides  for  the  pur- 
pose of  reducing  the  friction  is  to  invite  trouble.  Such  a  design 
makes  it  more  difficult  to  sink  the  caisson  plumb,  and  is  apt  to 
increase  instead  of  decrease  the  friction  by  allowing  boulders 
to  roll  into  the  open  space. 

Practically  all  working-chamber  sides  are  constructed  of 
two  forms:  namely,  that  in  which  the  vertical  section  is 
V-shaped,  and  composed  of  two  walls;  or  that  in  which  the 
vertical  section  is  essentially  a  rectangle  and  composed  of  a 
single  wall.  The  former  has  the  advantage  of  being  more 
rigid  and  so  requires  less  bracing,  while  the  latter  has  the 
advantage  of  permitting  excavation  under  the  cutting  edge 
to  be  more  easily  made. 

In  the  V-shaped  form  the  space  between  the  outer  and 
inner  walls  may  be  built  solid  with  timber,  as  was  done  in  the 
east  abutment  caisson  of  the  St.  Louis  arch  bridge;  or  it  may 
be  made  hollow  and  afterward  filled  with  concrete,  as  was  done 


2Q4  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  VIII 

in  most  of  the  caissons  designed  by  G.  S.  M  ORISON,  a  typical 
form  of  which  is  shown  in  Fig.  930.  Here  the  outer  wall  was 
made  of  i2Xi2-inch  timbers,  sheathed  on  the  outside  with 
two  layers  of  planking,  the  outer  one  running  vertically  and  the 
inner  one  diagonally.  The  inner  wall  consisted  of  a  single 
thickness  of  i7Xi7-inch  timbers  sheathed  with  4-inch  planks 
and  tied  to  the  outer  wall  with  rods. 

The  St.  Louis  Municipal  bridge  caissons,  Fig.  93^,  had  out- 
side walls  of  i  oX  1 2-inch  timbers,  sheathed  with  two  courses  of 
planking:  one  3Xi2-inch,  running  diagonally,  and  the  other, 
2 X i2-inch,  running  vertically,  the  latter  being  on  the  outside 
to  reduce  friction  in  sinking.  The  inner  wall  was  formed  of 
4X1 2-inch  horizontal  planks,  stepped  and  supported  at  inter- 
vals of  10  feet  on  vertical  struts.  The  small  size  of  material 
used  in  this  wall  was  made  possible  by  reinforcing  the  concrete 
in  the  space  between  the  walls.  Stepping  the  wall  made  it 
possible  to  count  on  the  horizontal  projection  of  this  inner  wall 
as  taking  load  when  the  caisson  was  filled  with  concrete  and  in 
its  final  position.  This  cannot  be  done  when  the  wall  is  on  a 
slope.  A  further  advantage  is  that  the  projections  gave  better 
control  of  sinking,  there  being  less  danger  of  sudden  drops  than 
when  the  wall  is  sloped. 

The  rectangular  section  of  side  wall  is  used  more  widely  than 
the  triangular,  on  account  of  the  facility  with  which  the  spoil 
near  the  sides  may  be  excavated.  Figs.  -930  and  /  illustrate  a 
good  example  of  this  type.  It  is  composed  of  a  double  thick- 
ness of  horizontal  i2Xi2-inch  timbers,  separated  by  a  single 
thickness  of  vertical  i2Xi2-inch  timbers,  some  of  which  extend 
up  beyond  the  caisson  to  form  a  part  of  the  crib.  Both  the 
outside  and  inside  faces  of  the  wall  are  faced  with  3Xi2-inch 
planks.  Figs.  936,  c  and  d  also  illustrate  the  same  type. 

ART.  95.    DETAILS  OF  CUTTING  EDGE 

The  cutting  edge,  as  the  part  of  the  caisson  which  rests  on 
the  ground  is  called,  must  be  designed  to  serve  four  functions: 
First,  it  must  be  sufficiently  strong  and  tough  to  stand  the 


ART.  95 


DETAILS    OF   CUTTING   EDGE 


295 


strains  and  abrasive  action  of  sinking;  second,  it  must  be  of  a 
form  which  will  allow  the  caisson  to  sink  readily  without 
excavating  under  the  cutting  edge;  third,  it  must  have  bearing 
surface  enough  to  prevent  sudden  sinking  when  a  soft  stratum 
is  encountered;  and  fourth,  it  should  be  so  designed  that  air 
cannot  readily  escape  under  the  same.  To  fulfill  the  first 
requirement  the  cutting  edge  is  usually  made  of  some  tough 
and  strong  wood,  such  as  elm,  or  else  is  shod  with  a  metal 
plate  or  piece  of  tough  wood.  The  second 
and  third  are  conflicting  requirements;  for 
the  second  »  true  knife  edge  is  the  ideal 
form,  while  for  the  third  a  considerable 
breadth  of  bearing  is  desirable.  As  con- 
structed, the  width  will  vary  from  about  4 
inches  to  18  inches.  To  meet  the  fourth 
requirement,  a  vertical  plate  extending 
about  6  inches  below  the  cutting  edge  is 
often  used.  Where  the  soil  is  dense  this 
plate  may  be  dispensed  with. 

Many  engineers  at  present  favor  the 
blunt  cutting  edge  in  preference  to  the  sharp  one.  T.  K. 
THOMSON'S  experience  is,  that  where  the  knife  edge  is  needed, 
i.e.,  in  hard  material,  to  allow  getting  close  to  the  outside  edge 
for  excavating,  it  would  cost  too  much  to  make  the  cutting 
edge  strong  enough,  and  where  the  material  is  soft  a  knife  edge 
is  not  needed. 

Fig.  93 d  illustrates  the  use  of  a  timber  wearing  plank  on  the 
cutting  edge.  It  was  6X12  inches  in  section,  the  main  timber 
forming  the  cutting  edge  being  30X30  inches  in  section,  while 
the  upper  inner  corner  of  the  latter  was  rebated  9  inches  to 
form  a  seat  for  the  feet  of  the  vertical  wall  timbers.  The 
advantage  of  a  timber  over  a  metal  cutting  edge  lies  in  less  time 
being  required  to  obtain  it,  and  in  the  greater  ease  with  which 
it  may  be  replaced  when  broken. 

The  form  of  cutting  edge  used  by  G.  S.  MORISON,  illustrated 
in  Fig.  950,  consisted  of  a  horizontal  and  vertical  plate,  the 
latter  being  stiffened  at  intervals  and  fastened  to  the  horizontal 


FIG.  950. — Details  of 
Cutting  Edge. 


296 


PNEUMATIC   CAISSONS   FOR  BRIDGES 


CHAP.  VIII 


plate  by  steel  diaphragms,  which  are  stiffened  on  the  edges  by 
three  angles.  The  horizontal  plate  extended  under,  and  was 
fastened  to  both  the  lower  surf  ace  of  the  bottom  timbers  and  the 
lower  edge  of  the  outside  sheathing,  while  the  vertical  plate 
was  fastened  to  the  same  outside  sheathing.  Near  the  bottom 
the  vertical  plate  was  reinforced  with  two  others.  Fig.  930 
shows  the  appearance  of  this  cutting  edge  in  place. 

The  bottom  timber  of  the  caisson  shown  in  Fig.  93  /  extended 

but  beyond  the  timbers  above  to 
protect  the  lower  edges  of  the  out- 
side sheathing,  while  it  in  turn  was 
protected  by  steel  plates  on  all 
sides  but  the  top.  This  form  of 
construction,  having  a  vertical 
plate  on  the  outside  and  a  hori- 
zontal angle  with  its  vertical  leg 
down  and  fastened  by  rivets  to  the 
vertical  plate,  and  with  its  hori- 
zontal leg  fastened  to  the  lower  sur- 
face of  the  lower  timber,  is  widely 
used,  but  is  not  economical. 

The  cutting  edge  of  the  caisson 
used  in  the  Kinzie  St.  draw-bridge, 
Chicago,  was  formed  with  an  8- 
inch  channel  iron  laid  horizontally 
with  flanges  turned  up  as  shown  in  Fig.  95^.  The  same 
general  form  was  used  on  the  Broadway  bridge  caissons  (Fig. 
93/0  >  the  only  difference  being  that  in  the  latter  case  the 
cutting-edge  timber  extended  out  to  protect  the  bottom  of 
the  sheathing,  while  in  the  former  case  the  channel  iron  served 
this  purpose.  This  form  of  metal  cutting  edge  is  the  most 
economical  and  was  designed  in  1901  by  T.  K.  THOMSON. 

ART.  96.    BRACING  OF  CAISSON 

Every  caisson  requires  more  or  less  bracing;  the  larger  and 
higher  it  is  the  more  bracing  will  it  require.     This  bracing  may 


Detail    of    Cu-tHnq    Edqe. 
(Enlarged.) 

FIG.  956. 


ART.  96  BRACING  OF    CAISSON  297 

• 

be  in  the  form  of  struts  and  tiers  near  the  bottom,  running 
horizontally  the  length  and  breadth  of  the  caisson,  or  it  may 
be  in  the  form  of  bulkheads,  or  trusses.  The  latter  two 
usually  serve  the  added  purpose  of  supporting  the  roof. 

The  bracing  in  the  33X90- foot  caisson  of  the  St.  Louis 
Municipal  bridge,  shown  in  Figs.  93^*  and  ;',  consisted  of  eight 
transverse  and  two  longitudinal  lines  of  horizontal  12X1 2-inch 
struts  spaced  about  10  feet  apart,  with  ij-inch  adjustable 
rods  on  both  sides  of  each  strut.  The  struts  at  their  inter- 
sections were  braced  with  vertical  i2Xi2-inch  timbers  and 
pairs  of  f -inch  rods  extending  to  the  deck  of  the  caisson.  A 
similar  form  of  bracing  was  employed  in  the  Belief  on  taine 
bridge  caissons,  as  illustrated  in  Fig.  930,  as  well  as  in  the 
Broadway  bridge  caissons,  Figs.  930  and/. 

The  south  main  pier  caisson  of  the  New  Quebec  bridge, 
55X180  feet  in  plan,  was  divided  by  timber  bulkheads,  as 
shown  in  Figs.  936  and  c,  into  eighteen  rectangular  compart- 
ments approximately  19X25  feet  in  size.  These  longitudinal 
and  transverse  bulkheads  were  respectively  24  and  12  inches 
thick,  except  the  lower  course  which  was  12  inches  thicker. 
All  extended  from  the  ceiling  to  about  the  top  of  the  cutting 
edge.  Each  transverse  bulkhead  was  trussed  by  a  pair  of 
adjustable  diagonal  rods,  the  ends  of  which  took  bearing  in  the 
end  walls  at  roof  level,  through  beveled  washers;  in  the  center 
they  bore  on  steel  plates,  the  latter  in  turn  bearing  on  both 
longitudinal  and  transverse  bulkheads.  The  end  walls  on 
each  side  of  the  longitudinal  bulkhead,  were  braced  by  a 
solid- web  knee  brace  1 2  inches  thick,  reaching  from  the  cutting 
edge  to  the  top  of  the  first  transverse  bulkhead.  Between 
bulkheads  the  sides  were  knee-braced  to  the  roof  by  single  and 
double  12X1 2-inch  struts  inclined  at  an  angle  of  45  degrees. 

The  bulkheads  of  the  east  abutment  caisson  of  the  St.  Louis 
arch  bridge  were  of  very  massive  construction,  being  made  of 
eight  horizontal  courses  of  timber,  the  upper  course  having 
eight  timbers  in  it,  making  a  width  of  10  feet,  while  the  bottom 
course  had  three  timbers,  making  a  width  of  3^  feet.  The 
numbers  varied  in  the  horizontal  courses  between  these  two 


298  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  VIII 

values  in  such  a  way  as  to  give  a  V-shaped  section  of  bulkhead. 
The  height  was  9  feet. 

A  longitudinal  wooden  truss  was  used  to  brace  the  31X79- 
foot  caisson  of  the  Havre  de  Grace  bridge.  It  was  6  feet  deep, 
the  upper  and  lower  chords  being  composed  of  two  pieces  of 
12X1 2-inch  timbers.  The  web  members,  both  vertical  and 
diagonal,  were  composed  of  timber  struts  and  diagonal  rods,  the 
latter  extending  through  the  first  deck  course  of  the  caisson. 
Cross  braces  were  placed  between  the  bottom  chord  of  the 
truss  and  the  side  walls. 

ART.  97.     CRIB  CONSTRUCTION 

Some  writers  consider  the  crib  as  a  part  of  the  caisson,  but 
since  the  crib  may  sometimes  be  dispensed  with  and  the  pier 
built  directly  on  the  caisson,  it  will  avoid  confusion  by  separat- 
ing the  two.  A  certain  height  of  crib  is  often  built  as  an  integral 
part  of  the  caisson  to  facilitate  floating  the  structure  into  place. 
The  purpose  of  the  crib  is  two-fold:  First,  it  serves  as  a  form 
for  the  concrete;  and  second,  it  serves  temporarily  as  a  coffer- 
dam to  keep  out  the  water.  If  the  masonry  or  concrete  work  is 
kept  sufficiently  in  advance  of  the  sinking  the  crib  may  some- 
times be  dispensed  with,  but  this  is  sledom  done  because  it 
brings  too  much  weight  on  the  caisson.  The  crib  is  a  per- 
manent part  of  the  foundation  and  usually  its  walls  are  a  con- 
tinuation of  the  walls  of  the  caisson,  perhaps  slightly  modified. 
The  crib  is  thoroughly  braced  with  longitudinal  and  transverse 
timbers  left  permanently  in  place. 

Although  it  is  customary  to  fill  the  crib  with  concrete,  yet 
under  some  circumstances  this  may  not  be  done.  In  the 
substructure  for  Pier  2  of  the  Memphis  bridge,  where  the  na- 
ture of  the  soil  made  it  necessary  that  the  load  on  the  founda- 
tion bed  be  kept  down  to  a  minimum,  the  pockets  near  the 
walls  in  the  crib  were  left  empty,  while  for  about  15  feet  down 
from  the  top  of  the  crib  a  solid  timber  grillage  was  used,  thus 
decreasing  the  weight  of  the  structure  very  considerably. 

The  crib  for  the  south  main  pier  of  the  New  Quebec  bridge 


ART.  97  CRIB   CONSTRUCTION  299 

had  a  wall  made  of  a  single  thickness  of  horizontal  i2Xi2-inch 
timbers  to  a  distance  of  25  feet  above  the  cutting  edge  of  the 
caisson,  braced  by  inside  vertical  12X1 2-inch  timbers,  spaced 
as  shown  in  Figs.  936  and  c,  the  latter  being  extensions  of  certain 
of  the  vertical  timbers  forming  the  sides  of  the  caisson.  The 
outside  was  sheathed  with  the  same  material  as  used  for  the 
caisson.  The  walls  were  braced  with  horizontal  longitudinal 
and  transverse  struts  24  inches  apart  vertically,  up  to  a  height 
of  25  feet  above  the  cutting  edge  of  the  caisson,  dividing  the 
crib  into  ninety  pockets  approximately  10  feet  square.  A 
similar  bracing  course  was  placed  29  feet  above  the  cutting 
edge  of  the  caisson;  above  this  point  there  was  no  bracing,  it 
being  replaced  with  a  concrete  retaining  wall  reaching  to  the 
top  of  the  crib,  built  against  the  walls  of  the  latter  and  battered 
on  the  interior  face,  increasing  in  thickness  from  the  top  down. 
This  was  placed  early  in  order  to  allow  it  to  harden  before  any 
stress  was  put  upon  it.  The  advantage  of  this  retaining  wall  is 
that  it  made  the  upper  part  of  the  crib  a  solid  monolithic  mass  of 
concrete. 

The  crib  shown  in  Fig.  930  had  the  bracing  carried  to  the  top 
and  was  notable  on  account  of  the  manner  in  which  the  bracing 
was  tied  together  with  vertical  rods.  Here  the  lower  courses 
of  bracing  helped  to  carry  the  roof  loads;  for  this  reason  the 
part  of  the  crib  up  to  the  top  of  the  rods  passing  through  the 
roof  may  be  considered  a  part  of  the  caisson. 

The  walls  of  the  cribs  for  the  St.  Louis  Municipal  bridge 
piers  consisted  for  the  most  part  of  one  thickness  of  loX  1 2-inch 
timbers,  sheathed  on  the  outside  with  one  layer  of  3-inch  diag- 
onal and  one  layer  of  3-inch  vertical  planks.  The  bracing 
consisted  of  vertical  12X1 2-inch  timbers  and  of  eight  rows  of 
horizontal  transverse  and  two  of  horizontal  longitudinal  loX  12- 
inch  timbers.  As  shown  in  Fig.  93^'  a  large  amount  of  3X10- 
inch  diagonal  bracing  was  also  used,  giving  a  truss-like  action 
to  the  bracing  and  greatly  strengthening  it. 

The  crib  construction  of  the  Broadway  bridge  is  shown  in 
Figs.  93<>  and/;  the  detail  are  so  simple  that  no  explanation  is 
necessary. 


300  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  VIII 

ART.  98.     COFFERDAM  CONSTRUCTION 

Both  durability  and  appearance  require  that  no  part  of 
the  crib  extend  above  low- water  level;  and  moreover,  to  keep 
the  obstruction  to  the  current  as  small  as  possible,  the  crib  is 
stopped  and  the  pier  commenced  at  a  considerable  distance 
below  low  water.  In  some  cases,  where  the  current  has  a  high 
velocity,  the  pier  is  started  at  or  below  the  river  bed,  or  the  upper 
part  of  the  crib  is  built  with  pointed  ends.  For  these  reasons, 
unless  conditions  are  such  that  the  pier  construction  can  be 
kept  well  above  water-level,  a  cofferdam  in  which  to  build  the 
pier  becomes  necessary.  Ordinarily  cofferdams  may  be  dis- 
pensed with  only  when  the  construction  is  carried  on  at  low 
water  stages  or  when  the  friction  and  resistance  to  sinking  is 
large.  As  a  general  rule  it  is  desirable  to  keep  the  weight  on  the 
caisson  *as  small  as  possible  as  this  affords  better  control  of 
the  sinking.  Even  when  possible  many  engineers  prefer  not 
to  start  building  the  pier  until  the  caisson  is  sunk  to  final  position, 
for  only  at  such  a  time  can  the  masonry  be  started  in  the  correct 
position.  The  walls  of  the  cofferdam  are  usually  made  of 
lighter  construction  than  those  of  the  crib,  but  it  is  always 
thoroughly  caulked,  and  braced  by  struts  running  the  length 
and  breadth  of  the  structure.  As  the  pier  is  built  up  these  braces 
are  removed  and  the  walls  are  braced  against  the  pier.  On  the 
completion  of  the  latter  the  cofferdam  is  removed,  if  not  the 
whole  structure,  at  least  that  part  above  low  water. 

Figs.  93  &  and  /  illustrate  the  cofferdam  used  for  one  of  the 
piers  of  the  St.  Louis  Municipal  bridge.  The  left  dotted  lines 
represent  the  top  course  of  crib  and  the  right  dotted  lines  the  top 
of  struts.  The  cofferdam,  which  was  33  feet  yj  inches  long, 
consisted  of  a  frame  of  horizontal  6  X  8-inch  and  vertical  6X6- 
inch  timbers,  sheathed  with  2Xi2-inch  planks.  It  was  braced 
with  6  X  8-inch  struts,  4  feet  apart  vertically,  and  in  rows  about 
10  feet  apart  horizontally. 

The  cofferdam  used  for  the  Brooklyn  pier  of  the  Manhattan 
bridge,  New  York,  N.  Y.,  was  one  of  the  highest  that  has  ever 
been  used  in  pneumatic  caisson  work,  being  44  feet  high  and 


ART.  99  PNEUMATIC   CAISSONS   OF   CONCRETE  301 

about  75X144  feet  in  plan.  It  was  built  in  three  sections, 
the  sides  of  the  first  two  sections  being  made  of  10X1 2-inch 
horizontal  timbers  laid  close  and  supported  by  i2Xi8-inch 
verticals,  spaced  12  feet  apart.  On  the  outside  two  layers  of 
3 X i2-inch  sheathing  were  placed,  the  inner  planking  being 
horizontal  and  the  outer  vertical.  The  upper  section  differed 
from  the  others  only  in  having  8Xi2-inch  instead  of  ioX  12- 
inch  horizontals. 

ART.  99.     PNEUMATIC  CAISSONS  or  CONCRETE 

Pneumatic  caissons  built  entirely  of  concrete  have  been'used 
to  some  extent  in  Europe,  but  in  this  country  the  nearest 
approach  to  the  all- concrete  pneumatic  caisson  are  those  for  the 
Beaver  bridge,  described  in  Art.  90.  As  there  explained  most 
of  the  sinking  was  done  by  the  open-well  method.  With  the 
exception  of  a  very  few  cases,  like  the  one  just  noted,  the 
tendency  in  this  country  has  been  to  use  wood,  but  at  the  same 
time  to  decrease  the  amount  formerly  used  by  reinforcing  the 
lower  part  of  the  crib  concrete,  as  was  done  in  the  St.  Louis 
Municipal  bridge  caissons.  A  covering  of  timber  offers  three 
advantages:  First,  it  avoids  the  necessity  of  waiting  for  the 
concrete  to  harden  before  commencing  sinking  operations; 
second,  it  offers  less  resistance  to  sinking  because  of  the  reduced 
friction  on  the  sides;  and  third,  it  forms  a  protection  in  sinking 
for  the  concrete  of  the  sides. 

The  pneumatic  process  was  used  during  the  final  part  of  the 
sinking  of  the  Beaver  bridge  caissons  in  order  that  the  bottom 
might  be  thoroughly  cleaned,  as  well  as  to  permit  laying  the 
concrete  filling  in  air.  The  caisson  was  changed  from  the  open 
to  the  pneumatic  type  in  the  following  manner:  It  was  first 
freed  of  water  down  to  a  level  which  permitted  the  placing  of 
horizontal  wooden  frames  in  each  of  the 'wells  at  an  elevation 
of  about  9  feet  above  the  cutting  edge.  Concrete  was  then 
placed  on  these  forms,  filling  the  wells,  the  first  7  feet  being 
allowed  to  harden  for  a  week  before  placing  the  rest.  At  the* 
center  of  each  well  a  vertical  shaft,  3  feet  in  diameter,  was 


302  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  VIII 

placed  to  form  a  means  of  communication  between  the  working 
chamber  and  the  outside. 

ART.  100.     PNEUMATIC  CAISSONS  or  METAL 

The  abundance  of  timber  in  America  has  limited  the  use  of 
the  metal  type  to  relatively  few  cases,  while  in  Europe  it  has 
been  extensively  used. 

The  river  piers  of  the  St.  Louis  arch  bridge,  the  first  structure 
in  this  country  founded  on  large  pneumatic  caissons,  rest  on 
metal  caissons.  Two  reason  may  be  given  for  this  fact:  First, 
there  was  considerable  uncertainty  as  to  the  action  of  a  timber 
roof  when  subjected  to  the  horizontal  thrust  from  the  super- 
structure; and  second,  timber  had  not  been  used  in  caisson 
construction  to  serve  as  a  precedent. 

The  caisson  for  the  east  pier,  which  was  hexagonal  in  plan, 
with  over- all  dimensions  of  60X82  feet,  had  walls  of  wr ought- 
iron  plates  f  inch  thick,  braced  with  iron  brackets  extending 
from  the  bottom  to  the  top,  and  spaced  i\  feet  apart.  The  roof 
was  formed  of  |-inch  iron  plates  riveted  to  the  lower  flanges 
of  thirteen  parallel  iron  girders,  spaced  5  feet  6  inches  apart. 
It  was  also  supported  by  two  heavy  bulkheads  of  oak  timber, 
7  feet  high,  in  the  air  chamber.  These  strong  supports  for  the 
roof  were  necessary  because  the  latter  had  to  take  the  entire 
weight  of  a  loo-foot  height  of  stone  masonry. 

The  walls  of  the  caisson  extended  above  the  roof  to  form  an 
enclosure,  in  which  the  masonry  was  laid.  No  monolithic  con- 
crete was  used  in  this  structure.  For  some  distance  up  the 
masonry  covered  the  entire  cross-section  of  the  crib,  but  above 
this  it  was  stepped  off,  the  space  between  the  iron  envelope  and 
the  masonry  being  braced  with  timbers  and  filled  with  sand. 
For  the  west  pier  caisson  the  iron  envelope  was  carried  up  but 
20  feet,  after  which  the  masonry  was  laid  in  the  open,  care 
being  taken  to  keep  the  top  of  the  same  above  water-level. 

The  metal  pneumatic  caissons  for  the  Alexander  III  bridge, 
Paris,  France,  built  in  1897,  are  among  the  largest  of  any  type 
ever  used.  In  plan  one  caisson  had  the  shape  of  a  parallelogram 


ART.  100  PNEUMATIC   CAISSONS   OF   METAL  303 

(the  angle  being  84  degrees),  the  length  of  the  sides  being 
approximately  145  and  no  feet,  transversely  and  parallel, 
respectively,  to  the  axis  of  the  bridge.  The  working  chamber 
had  a  clear  height  of  6.23  feet  and  through  this  extended  four 
transverse  girders,  each  6.23  feet  high,  their  bottoms  forming 
cutting  edges,  and  dividing  the  chamber  into  five  subchambers. 
On  their  upper  flanges  these  girders  supported  twenty-seven 
longitudinal  girders,  5.2  feet  deep,  which  carried  the  roof  of  the 
steel-plate  platform  that  formed  the  deck  of  the  caisson  proper. 
The  transverse  girders  had  solid-plate  webs  for  nearly  one-third 
of  their  length  at  each  end  and  open  web  members  in  the  central 
part.  The  longitudinals  were  ordinary  latticed  girders.  The 
working  chamber  had  a  roof  of  steel  plates  o.  2  inch  thick  which 
were  fastened  to  the  lower  flanges  of  the  longitudinal,  and  to  the 
upper  flanges  of  the  transverse  girders.  These  plates  did  not 
extend  horizontally  through  to  the  vertical  sides  of  the  caisson, 
but  at  the  sides  followed  down  the  inclined  end  posts  of  the 
transverse  girders,  and  at  the  ends  followed  the  knee  braces 
down  to  the  cutting  edge  to  give  sloping  inside  walls  on  all 
four  sides. 

Between  these  inclined  plates  and  the  outer  vertical  walls 
was  a  triangular  space  filled  with  concrete.  The  outside  wall 
plates  and  the  transverse  girders  were  all  stiffened  with 
knee  braces  extending  from  the  cutting  edge  to  the  longi- 
tudinal girders. 

The  outside  wall  plates  were  reinforced  on  the  lower  edges  by 
an  outside  vertical  plate  and  the  vertical  flange  of  an  inner  angle, 
while  the  transverse  girders  were  reinforced  for  bearing  and 
cutting  strains  by  adding  two  angles  riveted,  with  their  hori- 
zontal flanges  upward,  to  the  lower  edge  of  the  vertical  web 
plate  of  the  lower  chord.  The  cofferdam  above  was  19.7  feet 
high  and  was  composed  of  riveted  and  caulked  vertical  plates, 
0.118  inch  thick,  with  a  light  angle-iron  frame  and  light  inclined 
angle-iron  struts  from  near  the  upper  edge  and  the  middle  of 
the  top  of  the  transverse  girders.  The  total  distance  sunk  was 
27  feet  below  ordinary  water-level.  For  further  details  the 
reader  is  referred  to  either  Engineering  News,  vol  39,  page  254, 


304  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  VIII 

April   21,    1898,   or  Engineering  Record,   vol.   37,   page   275, 
Feb.  26,  1898. 

ART.  101.     CYLINDER  PIER  CAISSONS 

The  foundation  for  a  cylinder  pier  is  often  placed  by  the 
pneumatic  process,  in  which  case,  like  the  open-cylinder  caisson, 
there  is  usually  no  particular  point  at  which  the  caisson  may  be 
said  to  end  and  the  pier  begin.  The  pneumatic  cylinder  caisson 
is  very  similar  to  the  open  caisson  in  many  cases,  the  only 
difference  being  that  the  former  is  fitted  with  horizontal  dia- 
phragm doors  to  form  the  air-lock.  Often  a  part  of  the  sinking 
is  done  by  the  open-caisson  method  and  the  remainder  by  the 
pneumatic  method.  As  noted  in  Art.  92  the  cylinder  caisson 
was  the  first  type  of  foundation  to  which  the  pneumatic  process 
of.  sinking  was  applied  in  this  country. 

Fig.  loia  illustrates  the  cylinder  piers  and  pneumatic  cylinder 
caissons  used  for  the  Columbia  River  bridge  at  Trail,  B.  C. 
The  shells  were  of  steel  plates  from  rV  to  rV  inch  thick.  The 
lower  6 1  feet  were  formed  of  a  double  shell,  the  diameter  of 
the  inner  shell  being  3  feet,  and  that  of  the  outer  one  9  feet  at 
the  bottom  and  6  feet  at  the  top.  Beginning  at  a  point 
8  feet  above  the  bottom  of  the  caisson  the  inner  shell  was 
splayed  out  to  meet  the  outer  shell  at  the  cutting  edge,  thus 
forming  a  working  chamber  8  feet  high.  Near  the  bottom 
the  two  shells  were  braced  together  with  diagonal  lacing  as 
shown  in  the  diagram. 

The  upper  parts  of  the  cylinders  were  connected  and 
braced  by  two  vertical  transverse  rVX6o-inch  plates,  2  feet 
apart,  braced  together  and  the  space  between  the  two  filled 
with  concrete. 

The  air-lock  was  formed  by  placing  two  diaphragm  doors  in 
the  inner  shaft,  one  about  13  feet  above  the  cutting  edge  and 
the  other  at  a  point  about  16  feet  higher.  As  sinking  proceeded, 
a  third  door,  about  16  feet  above  the  second  door,  was  added, 
the  upper  two  doors  being  used  to  form  the  lock,  while  the  lower 
door  was  used  for  emergencies.  These  caissons  were  designed 


ART.  1 01 


CYLINDER   PIER   CAISSONS 


305 


SecHon  A- 

Horizontal  Top  Frame  lite 


Bracing       Frame  BoHofn  of  Pier  showing  Web 

FIG.   zoia. — Pneumatic  Cylinder  Caissons,  Trail,  B.  C. 


306 


PNEUMATIC   CAISSONS   FOR   BRIDGES 


CHAP.  VIII 


by  WADDELL  &  HARRINGTON,  and  may  be  considered  to  repre- 
sent current  standard  practice. 

In  the  repairs  of  the  Atchafalaya  River  bridge,  each  pier 
consisted  of  a  pair  of  8-foot  diameter  steel  cylinders,  filled  with 
concrete  and  braced  together  at  the  top  by  a  stiffened  web 
plate  or  diaphragm  about  20  feet  high,  as  shown  in  Fig.  loib. 
Each  cylinder  had,  in  addition  to  the  outer  8-foot  diameter 


>•• 

"~T 

r  — 

;-v 

1 

—  P 

i 

.«-•.• 

°-'r;  i 

v£i 

FIG.   1016. — Pneumatic  Cylinder  Caissons,  Atchafalaya  River  Bridge. 

shell,  an  inner  concentric  shell  5  feet  in  diameter,  with  a 
conical  section  uniting  it  with  the  cutting  edge  and  closing  the 
lower  end  of  the  annular  space  between  the  two  shells.  The 
shells  were  connected  by  four  stiff  webs.  The  inside  shell 
terminated  about  22!  feet  below  the  top  of  the  outer  one,  the 
latter  having  a  total  length  of  over  135^  feet  and  was  made  with 


ART.  102  COMBINATION   CYLINDER   CAISSONS  307 

5-foot  rings  erected  in  lo-foot  sections.  The  working  chamber 
was  25  feet  high,  and  had  a  roof  consisting  of  a  2-foot  oak 
diaphragm  made  of  four  thicknesses  of  timber,  with  a  circular 
hole  2  feet  in  diameter  closed  by  a  cast-iron  door. 

In  the  piers  of  the  Glasgow  bridge,  which  were  sunk  by  the 
pneumatic  process  the  diameter  of  the  outer  shell  was  15  feet, 
the  thickness  of  the  shell  at  the  base  being  ^  inch  and  at  the  top 
T5^  inch.  The  shaft  which  was  3  feet  7  inches  in  diameter 
formed  the  inner  cylinder,  and  this  was  removed  before  filling 
the  working  chamber  and  air-shaft. 

Almost  no  records  exist  of  the  use  of  the  reinforced-concrete 
pneumatic  cylinder  caisson.  In  Art.  102  there  is  given  an 
example  of  this  type,  in  which  the  first  part  of  the  sinking  was 
done  by  the  open-caisson  method  and  the  latter  part  by  the 
pneumatic  process. 

ART.  102.     COMBINATION  CYLINDER  CAISSONS 

With  the  cylinder  caisson  it  is  a  simple  matter  to  construct 
the  cylinder  to  be  used  either  as  an  open  or  a  pneumatic 
caisson.  This  makes  it  possible  to  utilize  the  advantages  of 
both  methods  of  sinking,  the  open  caisson  being  used  for  that 
part  of  the  sinking  in  which  the  material  can  be  dredged  or 
pumped  out,  and  the  pneumatic  process  for  that  part  where 
boulders  or  compact  material  is  met  with,  and  in  finally  prepar- 
ing the  foundation  bed  and  placing  the  concrete  filling  in  the 
working  chamber. 

The  caissons  for  the  Merrimac  River  bridge,  between 
Salisbury  and  Newburyport,  Mass.,  were  of  this  type,  Each 
caisson  consisted  of  an  8-foot  diameter  cast-iron  shell,  the 
metal  being  i  J  inches  thick  and  cast  in  8-foot  sections.  These 
sections  had  inside  flanges  bolted  together  and  a  mixture  of  red 
lead  and  linseed  oil  was  placed  between  the  joints. 

The  cylinders  were  sunk  by  inside  dredging  to  a  layer  of 
boulders  and  gravel.  They  were  then  loaded  with  pig  iron, 
air-locks  placed  on  top,  and  air  pressure  applied.  No  attempt 
was  made  to  sink  the  caissons  through  the  boulders,  but  instead 
a  novel  method  was  used  to  transform  this  boulder  and  gravel 


3o8 


PNEUMATIC   CAISSONS   FOR  BRIDGES 


CHAP.  VIII 


layer  into  a  good  foundation  bed.  The  pressure  in  the  cylinder 
was  reduced  a  little  allowing  about  a  foot  or  more  of  water  to 
rise.  Portland  cement  was  then  mixed  with  the  water  to  form 
a  grout,  which  was  kept  well  stirred  while  the  air  pressure  was 
increased  to  force  the  grout  into  the  gravel.  On  completion  of 
the  grouting  a  depth  of  from  10  to  20  feet  of  1-2-4  concrete 
was  laid  under  air  pressure,  and  allowed  to  harden,  after  which 
the  remainder  was  laid  in  the  open. 


FIG. 


io2a. — Pneumatic  Caissons  of  Reinforced  Concrete  for   Bronx   Viaduct  of 
New  York  Connecting  Railway 


Fig.  1020  shows  the  main  details  of  concrete  cylinder  caissons 
used  for  foundations  of  the  Bronx  viaduct  of  the  New  York 
Connecting  Railway.  The  caissons  varied  from  10  to  18  feet 
in  diameter  and  were  sunk  to  a  maximum  depth  of  55  feet. 
The  cutting  edge  was  formed  of  a  steel  angle  and  steel  plate,  and 
the  concrete  composing  the  caisson  was  well  reinforced  with 
vertical  and  horizontal  rods.  When  sinking  through  clay  the 
open  dredging  process  was  used,  while  in  passing  through 
quicksand  air-locks  were  placed  in  the  upper  part  of  the 
shafts  and  the  pneumatic  process  used. 


CHAPTER  IX 
PNEUMATIC  CAISSONS  FOR  BRIDGES 

ART.  103.     SHAFTS  AND  AiR-Locxs 

The  shafts,  which  form  the  means  of  communication  between 
the  working  chamber  and  the  outside,  are  circular  in  shape  and 
in  most  cases  are  of  steel  plate  f-inch  thick;  and  in  sections 
about  10  feet  long,  each  section  being  flanged  and  bolted  to  the 
one  above  and  below.  Separate  shafts  are  ordinarily  used  for 
men  and  materials,  those  for  the  men  being  about  3  feet  in 
diameter,  although  if  an  elevator  is  used  they  are  often  as  large 
as  6  feet  in  diameter.  The  shafts  for  the  removal  of  spoil  are 
about  2  feet  in  diameter.  Where  the  depths  are  only  moderate 
it  is  customary  to  have  a  ladder  built  in  the  shaft  used  by  the 
men,  but  when  the  depth  is  considerable  a  power  elevator  should 
always  be  employed  as  it  is  extremely  exhausting  to  climb  a 
long  distance  after  working  under  high  pressure.  The  men 
often  use  the  excavating  bucket  as  an  elevator. 

As  explained  in  Art.  92  the  air-lock  is  a  chamber  having  two 
doors,  one  of  which  opens  to  the  atmosphere  and  the  other  to 
the  working  chamber.  These  doors  are  so  placed  that  the 
unequal  air  pressure  will  always  force  them  against  their  seats, 
which  have  rubber  gaskets  to  prevent  the  escape  of  air.  The 
operation  of  the  lock  for  men  is  as  follows:  The  lower  door 
being  closed  and  the  upper  one  open,  a  man  enters;  the  upper 
door  is  then  closed  and  compressed  air  slowly  admitted  to  the 
lock,  and  as  soon  as  the  pressure  in  it  becomes  equal  to  that 
below,  the  lower  door  opens  allowing  the  man  to  enter  the 
working  chamber. 

The  air-lock  may  be  of  any  shape  and  of  any  desired  size, 
the  latter  depending  on  the  number  of  men  or  the  amount  of 
material  it  is  desired  to  lock  through  at  a  time.  The  material 
lock  is  often  but  a  section  of  the  shaft. 

309 


3io 


PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  IX 


A— 


Front  Elevation, 


Section  through  Center. 


Section  A-B. 

FIG.   io3a. Material  Lock  used  in  Pneumatic  Caissons  of  Memphis  Bridge,  1891. 


ART.  103 


SHAFTS    AND   AIR-LOCKS 


311 


In  the  early  caissons  the 
lock  was  placed  at  the  bot- 
tom of  the  shaft  and  ex- 
tended down  into  the  work- 
ing chamber,  but  at  pres- 
ent the  material  lock  is 
always  placed  at  the  top  of 
the  shaft,  while  the  man 
lock  is  placed  either  at  the 
top  or  some  distance  up 
from  the  bottom.  Caisson 
sinking  with  the  lock  at 
the  bottom  is  a  risky  un- 
dertaking because  a  'blow- 
out/ that  is,  a  sudden  out- 
rush  of  air,  will  cause  a 
like  inrush  of  water  ac- 
companied by  a  rapid  sink- 
ing of  the  caisson,  which 
is  almost  sure  to  damage 
the  lock.  With  the  lock 
out  of  commission  the  men 
in  the  working  chamber 
have  no  chance  to  escape, 
while  if  the  lock  is  at  the 
top  the  men  can  climb  up 
and  take  refuge  in  the  shaft 
above  the  level  of  the 
water.  About  the  only 
disadvantage  in  having  the 
lock  on  top  of  the  shaft  lies 
in  the  necessity  of  remov- 
ing it  each  time  a  new  sec- 
tion is  added  to  the  shaft; 
but  with  properly  designed 
connections  this  can  easily 
be  done,  and  without  dan- 


Vertical 

Section. 


rt 


Sectional     Plan. 

FIG.   1036. — Air  Lock  for  Men,  Memphis 
Bridge. 


3I2 


PNEUMATIC   CAISSONS  FOR  BRIDGES 


CHAP.  IX 


ger,  by  having  an  auxiliary  door  fitted  to  the  lower  end  of  the 
shaft  in  the  roof  of  the  working  chamber  which  is  closed 
when  the  lock  is  taken  off. 

Two  forms  of  air-locks  extensively  employed  for    caissons 
used   for    the   foundations   of   buildings   are   illustrated    and 


' 25'0" 


FIG.   103*:. — Arrangement  of  Air  Lock,  Shahs,  Pipes,  etc.      Bellefontaine  Bridge- 

described  in  Art.  119.  The  particular  advantage  which  these 
types  possess  is  that  the  bucket  may  be  lowered  into  the  air 
chamber,  filled  and  taken  out  without  detaching  from  the 
hoisting  rope. 

Another  form  of  material  lock  which  has  been  employed  is 
illustrated  in  Fig.  1030,  this  particular  one  being  used  on  the 
Memphis  bridge  caissons.  The  method  of  operation  is  de- 
scribed in  Art.  107.  The  essential  difference  between  this 


ART.  104  DESIGN  OF   CAISSONS  313 

and  the  types  described  in  Art.  119  lies  in  the  fact  that  here  the 
upper  door,  instead  of  being  in  a  horizontal  plane,  lies  in  a 
vertical  plane  at  B.  This  necessitates  either  dumping  the 
material  out  on  being  brought  to  the  top  or  else  the  bucket  must 
be  detached  from  the  cable  and  taken  out. 

The  form  of  lock  for  men  employed  on  the  above  mentioned 
bridge  is  illustated  in  Fig.  103^.  It  is  shown  in  position  in 
Fig.  103^.  luThe  upper  shaft  through  which  the  elevator- cage 
runs  is  a  cylinder  6  feet  in  diameter,  the  air-lock  itself  is  a 
cylinder  6  feet  in  diameter,  and  the  shaft  leading  to  the  caisson, 
a  cylinder  4  feet  in  diameter;  the  three  cylinders  are  tangent  to 
each  other,  and  the  shells  are  connected  by  cast-iron  door  frames 
carrying  doors,  while  a  fourth  door  opening  outward  was 
placed  at  the  bottom  of  the  lower  shaft;  in  working,  the  door 
between  the  two  shafts  was  always  kept  closed,  and  the  door 
at  the  bottom  of  the  bottom  shaft  was  always  left  open;  it  was 
possible,  however,  if  an  emergency  had  arisen  to  use  the  lower 
section  of  the  shaft  as  an  air-lock  in  itself;  when  the  filling  of  the 
working  chamber  was  completed  the  bottom  door  was  per- 
manently closed." 

ART.  104.    DESIGN  OF  CAISSONS 

It  is  impossible  to  compute  even  approximately  the  stresses 
in  the  various  parts  of  a  caisson  and  for  this  reason  it  is  best 
largely  to  follow  precedent.  Engineers  who  are  experts  on 
caisson  work,  have  built  many  caissons  and  by  observing  the 
weak  points  have  developed  strong  structures  with  increasing 
economy.  The  examples  given  in  the  preceding  articles  are 
representative  of  the  best  forms  in  use,  and  are  recommended 
to  the  careful  consideration  of  engineers  interested  in  this 
subject.  For  more  extended  information  the  reader  is  referred 
to  the  bibliography  in  Chap.  XIX. 

T.  K.  ThoMSON,  a  consulting  engineer  who  has  specialized  in 
pneumatic  caissons,  writes  on  their  design  as  follows: 

1  The  Memphis  Bridge,  by  GEO.  S.  MORISON. 


314  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  IX 

J"It  is  necessary  to  use  considerable  common  sense  and 
experience  in  attempting  to  calculate  the  strains  in  a  caisson. 
As  regards  the  deck,  for  example,  it  is  very  easy  to  calculate 
the  weight  to  be  carried  by  the  deck  and  the  strains  that  would 
result  therefrom,  and  we  know  that  the  air  pressure  acting  up 
against  the  roof  will  counterbalance  a  great  deal  of  this  weight, 
making  it,  in  fact,  something  like  a  pontoon  floating  in  the 
water.  But  on  the  other  hand,  the  air  pressure  is  often  slacked 
down  to  almost  nothing  in  order  to  overcome  the  friction,  and  is 
raised  again  before  much  water  has  time  to  enter  the  working 
chamber;  and  sometimes  an  accident  to  the  air  plant  will 
suddenly  cut  off  the  supply  of  air,  throwing  a  tremendous  strain 
on  the  roof.  If  the  principal  weight  on  the  roof  is  concrete  it 
will  in  many  cases  be  self-sustaining  unless  too  fresh. 

"The  same  with  the  sides.  If  the  material  were  absolutely 
homogeneous  all  around  and  the  caisson  were  sunk  absolutely 
plumb,  which  almost  never  happens,  and  the  air  pressure  were 
kept  just  equal  to  the  outside  pressure,  then  we  would  have 
practically  no  strain  on  the  sides — but  all  practical  caisson  men 
have  seen  the  sides  of  caissons  collapse,  and  some  very  strongly 
built  ones  at  that.  A  very  much  more  frequent  cause  of 
accident  than  loss  of  air  pressure  is  to  strike  some  obstruction 
on  one  side,  deflecting  the  cutting  edge,  and  thus  throwing 
much  of  the  weight  of  the  caisson  on  the  weakened  side,  making 
bad  worse.  .  „.•..- 

"in  building  wooden  caissons  I  very  seldom  halve  the  timbers 
or  use  dovetailed  joints,  preferring  to  use  butt  joints  as  much  as 
possible  with  plenty  of  drift  bolts.  The  trouble  with  butt  joints, 
however,  is  that  while  a  carpenter  will  make  a  dovetail  or 
half-lap  joint  fit  he  will  probably  leave  an  inch  or  so  play  in  a 
butt  joint. 

"The  deck  timbers,  as  well  as  those  in  the  sides,  should  be 
planed  on  one  side  and  one  edge,  for  the  sizes  would  otherwise 
vary  too  much  to  get  a  good  job,  while  the  planking  for  the 
outside  and  inside  of  the  air  chamber  should  be  either  tongue 
and  groove,  or  the  sides  should  be  planed  for  a  caulking  joint. 

1  See  "  Construction,"  Nov.,  1908. 


ART.  105  BUILDING   AND   PLACING   THE   CAISSON  315 

The  plank  should,  of  course,  have  its  faces  also  planed. " 
Since  very  many  drift  bolts  are  required  in  fastening  together 
the  heavy  timbers  in  wooden  caisson  construction,  it  is 
iesirable  to  adopt  the  proper  diameter  of  holes  to  be  bored. 
For  the  results  of  experiments  on  the  holding  power  of  drift 
bolts  and  the  best  ratio  of  the  diameter  of  hole  to  that  of 
bolt,  see  Art.  10  in  JACOB Y'S  Structural  Details. 

ART.  105.    BUILDING  AND  PLACING  THE  CAISSON 

The  caisson  may  be  built  on  ways  on  the  shore;  on  pontoons 
anchored  near  the  shore,  or  over  the  site  where  it  is  to  be  sunk; 
or  on  a  temporary  platform  supported  by  piles.  Of  the  three 
methods,  building  on  ways  on  the  shore  is  the  most  widely  used, 
but  to  make  this  method  satisfactory  the  following  conditions 
must  obtain:  First,  there  must  be  deep  water  near  the  shore; 
second,  the  soil  must  be  sufficiently  firm  to  hold  the  caisson, 
either  with  or  without  the  use  of  bearing  piles;  third,  there 
must  be  no  danger  of  a  high  and  rapid  rise  in  the  river; 
and  fourth,  the  shore  must  not  be  at  a  great  distance  from 
the  site  of  sinking. 

Where  satisfactory  shore  conditions  do  not  obtain  and  where 
the  water  is  deep  and  subject  to  sudden  rises  the  pontoon 
method  is  the  best.  Where  the  depth  of  water  is  not  great  and 
where  the  river  is  not  subject  to  considerable  changes  of  level 
the  method  of  using  a  temporary  platform  on  piling  is  con- 
venient. Caissons  for  abutments  and  buildings  may  usually 
be  built  directly  on  the  ground  near  the  site  where  they  are 
to  be  sunk. 

When  built  on  ways  the  caisson  sometimes  has  a  false  bottom 
fitted  to  it  to  reduce  the  depth  of  immersion,  and  a  sufficient 
height  of  crib  is  constructed,  preliminary  to  launching,  to 
insure  the  top  being  well  above  water-level.  After  launching 
and  towing  to  the  site  more  crib  is  added,  the  false  bottom 
removed  and  the  caisson  sunk  to  the  river  bed  by  placing 
concrete  in  the  crib. 

The  launching  ways  used  for   the  McKinley  bridge  over 


316  PNEUMATIC  CAISSONS   FOR  BRIDGES  CHAP.  IX 

the  Mississippi  River  at  St.  Louis,  Mo.,  consisted  of  a  number 
of  rows  of  piles  capped  with  timbers  running  at  right  angles  to 
the  river  and  on  a  slope  of  if  inches  per  foot.  Each  caisson  was 
built  on  shoes  extending  the  full  width  of  the  caisson,  the  long 
side  of  the  caisson  being  parallel  to  the  river,  and  each  shoe 
rested  on  a  cap  timber  on  which  it  slid  during  launching. 
These  shoes  were  spaced  about  6  feet  apart  and  were  so  made 
that  they  projected  down  over  the  sides  of  the  caps.  They 
were  bolted  to  the  latter  on  the  land  side  of  the  caisson.  The 
caisson  was  built  with  its  bottom  in  a  horizontal  position  by 
using  wedges  between  the  caisson  and  the  shoes.  The  launch- 
ing was  started  by  simultaneously  sawing  through  the  shoes 
below  the  bolts,  which  thus  allowed  the  caisson  to  slide  into  the 
water. 

Fig.  1 05 a  shows  the  caisson  for  one  of  the  piers  of  the  Van- 
couver bridge,  Vancouver,  Wash.,  as  it  was  being  built  on  the 
launching  ways.  The  general  scheme  was  about  the  same  as 
for  the  McKinley  bridge  caissons. 

Where  built  on  floats,  either  one  or  two  pontoons  may  be  used. 
Fig.  1056  shows  one  of  the  caissons  of  the  Willamette  River 
bridge  of  the  Northern  Pacific  Railroad  as  it  was  being  built 
between  two  barges  or  pontoons.  The  caisson  was  held  be- 
tween the  barges  until  a  height  of  20  feet  had  been  built  up, 
when  long  screws  were  attached  and  the  caisson  lowered  into  the 
water.  Two  heavy  trusses,  one  at  each  end,  tied  the  barges 
together  to  prevent  any  unequal  motion  of  the  latter  by  the 
waves.  Another  caisson  for  the  same  bridge  was  erected  on 
two  pontoons,  and  after  building  to  a  sufficient  height  the 
pontoons  were  scuttled  by  filling  them  with  water,  after  which 
they  were  pulled  out  from  under  the  caisson. 

The  78  X  144-foot  caisson  of  the  Manhattan  bridge  was  built 
in  a  pontoon  or  float,  84  feet  wide  and  150  feet  long,  which  had 
vertical  sides  8  feet  high.  The  float  was  built  of  3-inch  planks 
bolted  to  vertical  and  horizontal  timbers.  It  was  built  in  two 
halves  separated  by  a  longitudinal  joint  along  the  center  line. 
Blocking  was  set  up  on  the  floor  timbers  and  on  this  the  caisson 
was  built,  thus  making  the  latter  accessible  from  below.  On 


FIG.   105*3. — Caisson  on  Launching  Ways.     Vancouver  Bridge. 


FIG.  1056. — Cassion  Supported  between  Two  Barges.     Willamette  River  Bridge. 

(Facing  p.  316.) 


ART.  1 06  SINKING  THE   CAISSON  317 

completing  the.  caisson  the  joint  between  the  two  halves  of  the 
float  was  unlocked  and  sand  dumped  through  the  shafts  of  the 
caisson  to  the  floor  of  the  float  to  sink  the  halves  of  the  latter, 
after  which  the  same  were  pulled  from  beneath  the  caisson. 

Fig.  io5c  shows  one  part  of  the  4oXioo-foot  pontoon  of 
the  St.  Louis  Municipal  bridge  caissons  as  it  was  being  pulled 
from  beneath  the  caisson.  This  pontoon,  which  was  of  the 
same  type  as  that  described  above,  was  sunk  by  removing  plugs 
from  holes  in  the  bottom  of  the  pontoon. 

The  caissons  for  the  Passyiink  Ave.  bridge  piers  offer  a  good 
example  of  caissons  built  on  a  platform.  Sixteen  bearing  piles 
were  first  driven  in  two  longitudinal  rows  just  clear  of  the 
caisson  location.  These  were  capped,  and  from  these  cap 
timbers  four  equidistant,  transverse,  i4Xi6-inch  timbers  were 
suspended  by  pairs  of  i^-inch  rods,  16  feet  long,  threaded  the 
entire  length,  and  each  provided  with  two  nuts.  Each  trans- 
verse timber  was  held  by  means  of  a  steel  saddle  on  the 
under  side,  against  which  the  lower  nut  of  the  rod  bore  and  the 
other  nut  took  bearing  on  a  washer  on  top  of  the  pile  cap. 
The  transverse  timbers  were  first  screwed  up  tightly  against  the 
under  side  of  the  cap  timbers  and  on  these  the  caisson  was 
built.  After  building  the  cribs  to  a  height  of  about  26  feet 
the  caisson  and  transverse  timbers  were  gradually  lowered  by 
unscrewing  the  nuts  from  the  rods,  which  permitted  the  caisson 
to  float  in  its  exact  position. 

ART.  1 06.     SINKING  THE  CAISSON 

If  mud  covers  the  river  bottom  this  should  be  dredged  out 
before  placing  the  caisson  as  it  is  cheaper  to  remove  it  in  this 
manner  than  to  excavate  it  within  the  working  chamber. 
Great  care  must  be  exercised  in  grounding  the  caisson  to  place 
it  in  its  correct  position.  If  in  tidal  water,  this  may  be  done 
by  placing  concrete  in  the  crib  to  an  amount  which  will  just 
ground  the  caisson  at  low  tide.  Then,  by  means  of  tackles 
attached  to  clusters  of  piles  and  to  the  caisson  or  crib,  the 
structure  is  placed  in  its  true  position  at  high  tide  and  grounded 


318  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  IX 

as  the  water-level  lowers.  Concrete  is  then  poured  into  the  crib 
to  an  amount  which  will  prevent  floating  when  the  tide  rises. 
Often,  where  the  caisson  is  slightly  out  of  position,  it  may  be 
floated  by  admitting  a  small  amount  of  air  into  the  working 
chamber.  As  soon  as  enough  concrete  has  been  placed  to  put 
on  air  pressure  safely  to  expel  the  water  from  the  working 
chamber,  men  enter  to  commence  sinking  operations. 

In  clay  the  excavation  may  usually  be  kept  some  distance 
below  the  cutting  edge,  which  offers  the  advantage  of  allowing 
more  head-room  for  the  men.  This  cannot  be  safely  done  in 
sand  as  the  water  is  very  sensitive  to  changes  of  pressure 
and  so  it  is  not  possible  to  raise  the  pressure  very  much  from 
that  corresponding  to  the  head  on  the  cutting  edge.  In  one 
of  the  caissons  of  the  Rulo  bridge  a  test  well  was  sunk  in  clay 
17  feet  below  the  cutting  edge  without  any  increase  in  the  air 
pressure,  but  when  a  4-foot  vein  of  gravel  was  struck  the 
pressure  had  to  be  increased  8  to  10  pounds  at  once. 

In  sinking  caissons  the  load  is  at  first  usually  carried  on  the 
cutting  edge,  but  as  the  caisson  gradually  sinks  more  of  the 
load  is  resisted  by  friction  on  the  sides  and  less  by  bearing  on 
the  cutting  edge.  Contrary  to  the  usual  custom,  in  the  case  of 
the  55  X  i8o-foot  caisson  of  the  New  Quebec  bridge,  the  details 
of  which  are  shown  in  Figs.  936,  c,  and  d,  and  which  for  the  most 
part  was  sunk  through  sand,  the  load  was  not  at  any  time 
supported  on  the  cutting  edge. 

x"  Owing  to  the  great  size  of  the  caisson,  extraordinary  pre- 
cautions were  considered  necessary  to  provide  against  any 
unequal  settlement,  or  any  twisting  or  other  movement  of  the 
caisson,  which  might  tend  to  open  up  the  joints  and  seams  and 
consequently  allow  air  to  escape.  On  this  account  it  was 
decided  that  the  ordinary  method  of  sinking,  where  all  the  load 
is  carred  on  the  cutting  edge,  would  not  allow  the  movements 
of  the  caisson  to  be  sufficiently  controlled  during  the  actual 
sinking.  The  rather  unusual  method  was  therefore  employed 
of  carrying  the  entire  load  on  the  bulkheads  and  the  roof,  and 
no  load  at  all  on  the  cutting  edge. 

1  Engineering  News,  vol.  68,  page  854,  Nov.  7,  1912. 


ART.  107       REMOVING   SPOIL   FROM   WORKING   CHAMBER  319 

"The  caisson  was  supported  on  40  sand  jacks,  about  25  posts 
of  i2X i2-inch  yellow  pine,  and  54  sets  of  blocking.  The 
jacks  and  posts  bore  directly  against  the  roof,  while  the  blocking 
was  piled  under  the  bulkheads.  When  ready  for  a  drop  the 
blocking  and  posts  were  first  removed  by  washing  the  sand  from 
under  them  with  a  water-jet;  then  the  whole  caisson  was 
lowered  by  operating  all  the  sand  jacks  simultaneously.  The 
sand  jacks  were  of  simple  construction,  each  one  consisting  of  a 
29-inch  steel  cylinder  closed  at  the  bottom,  having  near  the 
bottom  two  3-iXich  holes  with  a  sliding  cover,  and  a  plunger 
consisting  of  a  single  piece  of  timber  fitting  easily  into  the 
cylinder.  The  cylinder  was  filled  two-thirds  full  of  sand,  the 
plunger  inserted,  and  its  upper  end  blocked  against  the  roof. 
The  operation  of  lowering  consisted  in  opening  the  lower  holes 
and  inserting  a  water-jet,  thus  washing  out  the  sand. 

"These  jacks  worked  admirably,  the  result  being  that  the 
caisson  was  sunk  absolutely  level  and  in  its  proper  location. 
Before  each  drop  a  trench  was  excavated  under  the  cutting 
edge  to  a  depth  of  2  or  3  feet,  and  filled  with  clay,  which  tended 
to  prevent  the  escape  of  the  air  and  also  acted  as  a  lubricant 
during  sinking.  This  scheme  was  followed  throughout  the  entire 
sinking  and  seemed  to  materially  facilitate  the  operation." 

Sinking  the  caisson  is  accomplished  by  excavating  the 
material  in  the  working  chamber  and  by  placing  concrete  in  the 
crib  to  weight  the  structure.  The  water-jet  is  sofrietimes 
employed  to  reduce  friction  on  the  sides. 

• 
ART.  107.     REMOVING  SPOIL  FROM  WORKING  CHAMBER 

Various  devices  have  been  developed  for  removing  the  spoil 
from  the  air  chamber.  Where  the  material  is  sand  the  blow-out 
process  or  mud-and-sand  pump  is  ordinarily  employed;  where 
clay  is  encountered  it  is  usually  best  to  remove  it  with  buckets, 
using  some  simple  form  of  air-lock,  or  perhaps  the  clay  may  be 
mixed  with  water  and  the  sand-and-mud-pump  process  used. 
Boulders  must  be  removed  through  the  air-locks. 

BLOW-OUT  PROCESS. — The  blow-out  process  is  a  very  simple 


320  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  IX 

affair,  the  principle  consisting  of  using  the  pressure  in  the  air 
chamber  to  drive  out  sand  or  mud  when  it  is  piled  around  the 
inlet  of  a  pipe  which  leads  from  the  working  chamber  to  the 
open  air.  The  diameter  of  the  pipe  is  usually  about  4  or  5 
inches,  the  top  being  fitted  with  an  elbow  to  throw  the  sand  in  a 
horizontal  direction,  while  the  lower  part  has  attached  to  it  a 
flexible  hose  of  large  diameter  with  a  valve.  To  blow  out 
the  sand  and  mud  it  is  only  necessary  to  heap  it  up  around  the 
mouth,  open  the  valve,  and  the  material  is  then  carried  out 
with  a  high  velocity;  in  fact  the  velocity  is  so  great  that  the  pipe 
rapidly  wears  away.  At  the  Havre  de  Grace  bridge  the  elbow, 
which  was  of  chilled  iron,  4  inches  thick,  was  worn  through  in 
two  days.  Considerable  care  must  be  exercised  in  placing  the 
material  against  the  inlet  for  if  a  considerable  amount  of  air  is 
not  admitted  with  the  sand  and  mud,  it  will  clog,  while  if  there 
is  too  much  air  admitted  it  is  a  waste.  It  has  been  found  ad- 
vantageous to  have  small  holes  in  the  pipe  above  the  inlet  as 
this  gives  more  uniform  action,  tending  to  draw  the  material  up 
instead  of  merely  driving  it  and  thus  lessening  the  amount  of 
air  entering  with  the  sand  and  mud.  Although  the  dry  blow- 
out is  a  very  rapid  and  satisfactory  means  of  removing  the 
spoil  from  the  working  chamber  it  has  some  disadvantages: 
First,  a  tendency  to  vary  the  pressure  in  the  working  chamber; 
and  second,  a  tendency  to  cause  rapid  wear  in  the  pipe  elbow  as 
noted  above.  The  lowering  of  the  pressure  due  to  the  air 
passing  up  through  the  pipe  causes  a  very  thick  fog,  making  it 
difficult  for  the  workmen  to  see.  It  is  also  apt  to  allow  the 
water  to  enter  from  the  outside.  On  the  other  hand,  if  the  air 
compressors  are  supplying  air  at  a  rate  sufficient  to  maintain  a 
constant  air  pressure  when  the  sand  is  being  blown  out,  on 
stopping  the  latter  operation  the  pressure  may  rise  to  a  point 
sufficient  to  cause  a  blow-out  under  the  cutting  edge,  which  is 
usually  followed  by  a  flooding  of  the  air  chamber.  Largely  on 
account  of  the  destructive  action  on  the  pipe,  and  for  the  added 
reasons  just  noted,  the  dry  blow-out  process  is  most  satisfactory 
when  the  pressure  in  the  working  chamber  is  fairly  low,  although 
a  head  of  at  least  20  feet  is  necessary.  This  process  is  said  to 


ART.  107       REMOVING   SPOIL   FROM   WORKING   CHAMBER 


32I 


have  been  used  first  by  WILLIAM  SOOYSMITH  in  1859  in  building 
bridge  piers  over  the  Savannah  River. 

SAND-AND-MUD  PUMP. — The  principle  involved  in  this  form 
of  excavator  is  that  of  the  induced  current,  where  a  quantity 
of  water  with  a  high  velocity  causes  a  reduction  of  pressure 
which  draws  the  mud  and  sand — well  mixed  with  water — into 
the  pipe.  Fig.  107  a  illustrates  the  form. used  on  the  Memphis 
bridge.  The  water  enters  at  the  side  under  a  high  pressure  and 
passes  up  through  the  small  annular  space,  at  which  point,  on 
account  of  the  high  velocity,  the  pressure  is  low.  The  lower 
part  of  the  pump  connects  with  a  pipe  or 
hose,  the  lower  end  of  which  rests  in  a  pool 
of  mud  or  sand  and  water.  On  account  of 
the  difference  of  pressure  at  the  two  ends  of 
this  pipe  the  mud  is  drawn  into  the  pump 
and  carried  upward  with  the  water,  through 
a  pipe  which  connects  with  the  top  of  the 
pump.  The  essential  difference  between 
this  form  of  excavator  and  the  blow-out 
process  is  that  in  the  former  the  water  is 
the  moving  force  doing  the  work  while  in 
the  latter  it  is  the  air  from  the  working 
chamber.  The  water  pressure  used  is 
ordinarily  about  80  pounds  per  square 
inch.  This  method  was  first  used  by  JAMES 
B.  EADS  in  the  caissons  of  the  St.  Louis 

FIG.  io7a. — Sand-and- 

arch  bridge.  Fig.  gia  illustrates  another  Mud  Pump.  Memphis 
form  of  the  sand-and-mud  pump. 

In  the  Williamsburgh  bridge,  New  York,  the  hose  was  extended 
to  a  sort  of  sump  in  the  bottom  of  the  excavation  where  its 
open  end  was  placed  below  the  surface  of  the  water.  Gravel,  sand 
and  mud  were  constantly  fed  into  the  nozzle  by  a  laborer  who 
raked  it  up  and  prevented  clogging,  and  another  man  with  a 
f-inch  nozzle  played  a  5o-pound  water-jet  against  the  soil  to 
wash  it  into  the  sump. 

For  a  description  of  this  process  as  applied  to  open-caisson 
work  the  reader  is  referred  to  Art.  91.  In  some  caisson  work  at 


Vertical    Section. 


Horizontal    Section. 


322  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  IX 

Arran,  Switzerland,  instead  of  using  a  sump  a  horizontal  hopper 
was  employed,  the  discharge  pipe  leading  from  the  lowest 
point  in  the  hopper.  A  jet  of  water  from  a  small  pipe  was  con- 
stantly played  on  the  material  as  it  was  fed  into  the  hopper. 

REMOVING  MATERIAL  WITH  BUCKETS. — Clay  is  usually  more 
cheaply  removed  with  buckets  than  by  any  other  method.  Large 
rocks  must  be  blasted  to  pieces  and  removed  with  buckets.  As 
stated  in  Art.  103  where  a  form  of  lock  similar  to  the  Moran  or 
O'Rourke  lock  is  used,  the  bucket  may  be  taken  from  the  lock 
without  removing  it  from  the  hoisting  rope.  In  the  form  shown 
in  Fig.  1030,  instead  of  running  the  hoisting  rope  to  an  engine  on 
the  outside,  the  hoisting  is  done  by  compressed  air  from  the 
working  chamber  working  in  the  cylinder  shown  on  the  left.  In 
this  cylinder  runs  a  piston,  the  two  sets  of  sheaves  being  so 
arranged  that  one  stroke  of  the  piston  lifts  the  bucket  the  whole 
distance. 

A  novel  device,  called  the  water  column,  was  used  in  the 
caissons  of  the  Brooklyn  bridge  to  remove  the  material.  It 
consisted  of  an  open  shaft,  the  lower  part  extending  into  a  sump 
which  was  kept  full  of  water  and  the  shaft  itself  was  filled  with 
water  up  to  a  point  sufficient  to  balance  the  air  pressure  in 
the  caisson.  Workmen  pushed  the  spoil  under  the  shaft  and 
from  there  it  was  removed  by  dredging  with  an  orange-peel  or 
clam-shell  bucket. 

ART.  1 08.     CONCRETING  THE  AIR  CHAMBER 

When  rock  is  reached,  if  the  same  is  level,  it  is  only  necessary 
to  clean  off  all  loose  material  before  depositing  the  concrete. 
On  the  other  hand,  if  not  level,  some  preliminary  work  must  be 
done;  if  the  rock  has  a  uniform  slope  it  should  either  be  blasted 
down  to  a  level  surface  or  else  stepped,  unless  very  rough ;  although 
if  the  rock  surface  is  at  practically  the  same  elevation  all  around 
the  cutting  edge  of  the  caisson,  but  irregular  within,  little 
more  than  a  thorough  cleaning  will  be  necessary.  For  those 
caissons  founded  on  clay  or  hard-pan  a  level  surface  is  easily 
obtained. 


ART.  109  RATE   OF   SINKING  323 

Caisson  No.  10  of  the  Passyunk  Ave.  bridge  landed  on  rock 
which  bad  a  slope  of  about  5  feet  in  the  length  of  the  caisson. 
As  soon  as  rock  on  the  high  side  was  reached,  the  cutting  edge 
on  the  low  side  was  blocked  with  6Xi2-inch  timbers,  6  feet 
apart,  after  which  excavation  under  the  cutting  edge  was 
carried  to  rock  and  extended  i|  feet  out  beyond  the  cutting 
edge.  This  excavation  was  then  filled  with  concrete. 

In  the  caissons  for  the  St.  Louis  Municipal  bridge  the  rock 
surface  was  irregular  but  no  attempt  was  made  to  level  it 
off  or  to  bring  the  caissons  to  bearing  throughout.  Where 
depressions  occurred  the  sand  was  removed  and  sacks  of  concrete 
were  deposited  on  the  rock  and  tamped  under  the  cutting  edge, 
after  which  concrete  was  placed  in  the  working  chamber  in  the 
usual  manner. 

The  concrete  for  filling  the  working  chamber  may  be  carried 
in  through;  the  material  shafts  and  locks  by  means  of  buckets, 
or  special  arrangements  may  be  made,  by  placing  a  cone-shaped 
frame  above  the  lower  door,  by  which  a  yard  or  more  of  concrete 
may  be  dumped  into  the  lock  through  the  upper  door.  The 
latter  is  then  closed  and  air  admitted  to  the  lock  allowing  the 
lower  door  to  open  and  the  mass  of  concrete  to  fall  through  the 
shaft  to  the  working  chamber.  The  conical  frame  prevents  the 
concrete  from  remaining  in  the  lock  when  the  lower  door  is 
opened.  For  a  description  of  the  method  used  in  placing  the 
concrete  in  the  working  chamber  see  Art.  186. 

ART.  109.     RATE  or  SINKING 

The  rate  of  caisson  sinking  varies  greatly,  the  larger  the 
caisson  and  the  harder  the  material  sunk  through,  the  slower 
the  rate.  Sinking  operations  are  usually  carried  on  day  and 
night,  and  the  rate  of  sinking  will  vary  from  almost  nothing 
where  beds  of  boulders  are  encountered  to  as  much  as  3  feet 
a  day  where  clean  sand  is  met.  Most  engineers  keep  a  chart 
of  the  progress  of  the  work;  Fig.  ioga,  which  illustrates  the 
progress  in  sinking  one  of  the  caissons  of  the  Kinzie  St.  draw- 
bridge, Chicago,  is  a  very  satisfactory  form  of  chart  to  use.  The 


3  24 


PNEUMATIC   CAISSONS   FOR  BRIDGES 


CHAP.  IX 


caisson  is  shown  in  Figs.  1096  and  c.  Instead  of  carrying  the 
whole  caisson  to  bedrock  the  cutting  edge  was  stopped  about 
half  way  down  and  wells  were  then  sunk  the  remainder  of  the 
distance. 

In  sinking  Pier  D  of  the  Memphis  bridge,  excluding  long 
delays,    an   average   rate   of    1.5    feet    per   day   of   24  hours 


FIG.   ioga. — Progress  of  Sinking  Caissons.     Kinzie  St.  Bridge,  Chicago. 

was  maintained  through  sand  and  only  0.31  foot  through 
clay,  while  for  Piers  2  and  5  of  the  Thebes  bridge  the  average 
rates  were  0.23  and  0.41  foot  respectively;  here  hard  gravel 
was  encountered. 


ART.   109 


RATE    OF    SINKING 


.325 


326 


PNEUMATIC   CAISSONS  FOR  BRIDGES 


CHAP.  IX 


The  rate  per  day  of  sinking  the  St.  Louis  Municipal  bridge 
caissons  varied  from  an  average  of  0.68  foot  for  Pier  4  to 
1.95  feet  for  Pier  3,  with  1.28  feet  as  an  average  for  all  caissons. 
The  best  progress  in  one  day  was  5.17  feet,  while  the  best 
seven-day  run  was  34  feet  or  4.86  feet  per  day.  For  the  caissons 

of  the  McKinley  bridge, 
St.  Louis,  the  average  rate 
for  all  caissons  was  2  feet 
per  day,  with  a  maximum 
of  7.7  feet  in  one  day. 


.Plan.' 

FIG.   lope. — (See  also  Fig.  1096.) 


FRICTIONAL 

RESISTANCE 

Estimating  the  probable 
frictional  resistance  to  be 
met  with  in  sinking  cais- 
sons is  one  of  the  most 
difficult  features  involved 
in  the  design.  It  depends 

upon  numerous  factors  such  as  the  kind  of  material  pene- 
trated; the  material  composing  the  sides  of  caisson  and  crib  ; 
depth  to  which  sunk;  whether  the  sides  of  the  caisson  are  ver- 
tical or  flared;  whether  or  not  the  water-jet  is  used;  and  the 
amount  of  air  leaking  under  the  cutting  edge. 

In  general,  the  frictional  resistance  per  square  foot  of  exposed 
surface  of  caisson  and  crib  will  seldom  be  less  than  250  nor  more 
than  800  pounds,  although  in  boulder-strewn  material  it  may  be 
as  much  as  1000  pounds.  Next  to  mud  and  silt,  sandy  soils 
offer  the  least  resistance,  especially  when  carrying  large  amounts 
of  water,  while  clay  will  offer  less  resistance  than  material  con- 
taining boulders.  With  uniform  soil  conolitions  the  unit  fric- 
tion will  increase  with  the  depth;  for  instance,  at  the  McKinley 
bridge,  which  crosses  the  Mississippi  River  at  St.  Louis,  the 
friction  was  found  to  be  about  300  pounds  per  square  foot  of 
exposed  surface  at  40  feet,  and  600  pounds  at  a  penetration  of 
70  feet.  Anything  which  tends  to  loosen  the  soil  around  the 


ART.  no 


FRICTIONAL  RESISTANCE 


327 


sides  of  the  caisson  and  crib  will  decrease  the  friction,  at  least  for 
a  short  time;  escaping  air  has  about  the  same  effect  as  the  water- 
jet  in  lubricating  the  material.  Although  flaring  out  the  bottom 
of  the  caisson  tends  to  reduce  the  side  friction,  yet,  on  account  of 
possible  wedging  action  by  material  falling  into  the  open  space 
above  the  bottom,  and  further,  on  account  of  the  loss  of 
guidance,  pneumatic  caissons  are  now  practically  all  made  with 
vertical  outside  walls. 

Table  No.  noa  gives  values  for  the  skin  friction  when  the 
caissons  were  well  down  for  a  number  of  notable  structures. 
Table  No.  no  b,  taken  from  an  article  by  H.  L.  WILEY  in  Trans- 
actions American  Society  of  Civil  Engineers,  vol.  62,  page 
113,  ^March,  1909,  gives  values  of  friction  for  both  open  and 
pneumatic  caissons. 


TABLE  NO.  noa 

SKIN  FRICTION  FOR  PNEUMATIC  CAISSONS  OF  BRIDGES 

(Expressed  in  Pounds  per  Square  Foot) 


Name  of  bridge 

Range  for 
separate 
piers 

Aver- 
age 

No. 
of 
piers 

Materials  penetrated  in  sinking 
caissons 

Belief  ontaine  

600—700 

648 

4 

Fine    sand,    sand,    coarse   sand, 

Blair  Crossing  
Brooklyn  

330-410 
600 

38l 

4 

boulders. 
Fine    sand,    coarse    sand,    clay. 

Cairo  .   . 

6  2  2—  0  3  2 

7^O 

IO 

Sand. 

Havre  de  Grace  
McKinley  

308-489 
600 

400 

4 

Silt,  sand,  mud. 

Memphis  
Miles  Glacier. 

365-837 
62O 

584 

5 

Sand,  gravel,  mud,  clay,  sedi- 
ment, very  tough  clay,  quick- 
sand. 

Nebraska  City  
New  Omaha  

409-590 
472-673 

525 
617 

3 
5 

Sand,  gravel,  some  clay  to  bed- 

Rulo. 

3<;i—  044 

614 

4 

rock. 
River  sand,  coarse  sand,  rubbish, 

Sioux  City  

314-535 

463 

4 

clay,  gravel. 
Fine  sand,  yellow  sand,  gravel, 

Williamsburg     

7"?o 

clay,  boulders. 

General  average  for  nine  bridges,  554  pounds  per  square  inch. 


328 


PNEUMATIC   CAISSONS   FOR   BRIDGES 


CHAP.  IX 


TABLE  NO.  1106 


No. 

Type  of  caisson 

Method  of 
sinking 

Material  penetrated 

Skin 
fric- 
tion 

Depth 
below 
low 
water 
in  feet 

Area  of 
base  in 
square 
feet 

i 

Cast  iron  

Open  excavation 

Gravel,  clay  

240 

60 

125 

2 

Cast  iron 

Open  excavation 

Sand   clay 

250 

75 

225 

3 

Cast  iron 

Open  excavation 

Sand 

250 

60 

125 

4 
5 

Wrought  iron  
Cast  iron 

Open  excavation 
Open  excavation 

Sand,  clay  
Sand   clay   gravel. 

285 
300 

140 
100 

IOOO 
125 

6 

7 

Cast  iron.  
Cast  iron 

Open  excavation 
Open  excavation 

Sand  

Silt 

325 
350 

60 

60 

125 
125 

8 

Steel  construction. 

Open  excavation 

Silt,  sand    clay 

375 

55 

190 

9 

Cast  iron 

Open  excavation 

Silt    mud   clay. 

39O 

75 

IOO 

10 

Timber  construction 

Open  excavation 

Sand 

4SO 

30 

1300 

II 

Steel  construction. 

Open  excavation 

Silt   clay 

450 

60 

700 

12 

Steel  construction. 

Open  excavation 

Silt   clay   sand 

450 

60 

I2OO 

13 

14 

Steel  construction.  .  . 
Steel  construction. 

Open  excavation 
Open  excavation 

Mud,  sand  
Clay 

450 
450 

65 

75 

1300 
1500 

IS 
16 

Iron  construction.  .  . 
Cast  iron 

Open  excavation 
Open  excavation 

Sand,  gravel,  clay  

Clay 

480 
50O 

65 
60 

200 
125 

17 

Steel  construction. 

Open  excavation 

Clay 

700 

65 

I3OO 

18 

Masonry 

Pneumatic 

Sand   mud 

205 

40 

75 

19 

Timber  construction 

Pneumatic 

Clay 

250 

35 

800 

20 

Steel  construction. 

Pneumatic 

Clay,  sand 

275 

60 

150 

21 

Timber  construction 

Pneumatic 

Silt   sand   mud 

310 

75 

2550 

22 
23 

24 
25 

26 

27 

Timber  construction 
Timber  construction 
Timber  construction 
Timber  construction 
Steel  construction.  .  . 
Timber  

Pneumatic 
Pneumatic 
Pneumatic 
Pneumatic 
Pneumatic 
Pneumatic 

Sand,  clay,  gravel..  .  . 
Sand,  clay,  boulders.  . 
Clay,  sand,  gravel.  .  . 
Sand,  gravel,  clay..  .  . 
Sand,  boulders  
Silt,  clay,  gravel 

350 
400 
400 
425 
450 
500 

100 

48 
95 
55 
68 

75 

1200 
1925 

4500 
1300 
2700 
1800 

28 

Iron  cylinder 

Pneumatic 

Sand,  shale  

525 

60 

1  200 

29 

Timber  construction 

Pneumatic 

Sand       

540 

75 

1700 

30 
31 
32 
33 

34 

Timber  construction 
Timber  construction 
Timber  construction 
Timber  construction 
Timber  construction 

Pneumatic 
Pneumatic 
Pneumatic 
Pneumatic 
Pneumatic 

Sand,  clay  
Sand,  gravel,  clay.  .  .  . 
Sand  '  
Sand,  boulders  
Silt,  sand,  clay  

600 
650 
650 
660 
900 

75 
8c 
90 

101 

45 

1400 

2000 
1200 
2100 
1700 

In  sinking  the  Commercial  Cable  Building  caissons  the  fric- 
tional  resistance  varied  from  250  to  300  pounds  per  square  foot 
of  exposed  surface,  while  in  the  United  Fire  Insurance  Co. 
caissons  it  was  as  high  as  1000  pounds. 

The  highest  value  of  frictional  resistance  was  observed  in 
1910  while  sinking  the  concrete  caisson  for  the  pivot  pier  of  the 
reconstructed  swing  bridge  of  the  Grand  Trunk  Railway  at 
Black  Rock  Harbor  on  the  Niagara  River.  The  material  pene- 
trated was  a  very  sticky  red  clay.  The  concrete  open  caisson 
weighed  8700  tons  and  1084  tons  of  stone  and  pig  iron  were 


ART.  in    PHYSIOLOGICAL   EFFECTS    OF    COMPRESSED   AIR  329 

piled  on  top  of  it.     The  area  was  10235  square  feet,  thus  giv- 
ing a  frictional  resistance  of  1912  pounds  per  square  foot. 


ART.  in.     PHYSIOLOGICAL  EFFECTS  OF  COMPRESSED  AIR 

The  question  of  the  physiological  effects  on  the  human  system 
when  working  in  compressed  air  is  an  important  one  from  both 
the  humanitarian  and  financial  standpoints.  In  the  past  almost 
all  the  important  works  employing  compressed  air  have  levied 
a  heavy  toll  of  suffering  and  death  on  the  'sand-hogs/  as 
caisson  workers  are  commonly  called.  For  instance,  on  the 
caisson  work  of  the  St.  Louis  bridge  there  were  119  cases  of 
so-called  caisson  disease,  with  14  deaths  from  the  same,  while 
on  the  Brooklyn  bridge  there  were  no  cases  of  illness,  with 
3  deaths.  These,  of  course,  were  early  examples;  at  the  pres- 
ent time,  owing  to  a  better  knowledge  of  the  disease,  the 
records  are  not  so  bad,  but  the  disease  still  claims  its  victims  in 
too  many  cases. 

No  harmful  effects  are  felt  on  entering  the  compressed  air, 
or  while  remaining  in  it;  only  during  decompression  or  after 
emerging  are  the  workmen  affected.  The  disease,  which  has 
been  proven  to  be  aeremia,  may  be  divided  into  two  classes: 
First,  that  in  which  the  attack  is  light;  and  second,  that  in  which 
it  is  severe.  The  first  form  is  characterized  by  very  severe 
pains,  chiefly  in  the  joints,  and  closely  resembles  rheumatism 
in  its  effects.  From  the  tendency  to  cause  its  victim  to  double 
up  in  agony  it  is  commonly  known  as  the  'bends.'  When 
the  attack  is  very  severe  it  usually  paralyzes  its  victim  and  is 
commonly  fatal. 

SENSATIONS  FELT  ON  ENTERING  THE  AIR  CHAMBER. — On 
entering  the  air-lock  and  having  the  air  pressure  turned  on, 
some  of  the  sensations  felt  are  heat,  slight  giddiness  and  head- 
ache, pain  in  the  ears,  breathlessness,  inability  to  whisper — 
caused  by  the  resistance  of  the  compressed  air  to  the  finer 
muscular  movements  of  the  tongue — and  a  feeling  of  resistance 
to  movement  owing  to  the  density  of  the  air.  A  slight  dis- 
comfort is  usually  felt  in  maintaining  equilibrium  between 


330  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  IX 

the  air  pressure  inside  and  outside  the  body,  the  most  painful 
being  in  the  ears,  as  noted  above.  This  may  be  overcome  by 
closing  the  mouth  and  holding  the  nose,  and  at  the  same  time 
trying  to  expel  the  air  from  the  lungs;  such  action  makes  the 
pressure  in  the  tympanic  cavity  equal  to  the  outside  pressure 
by  means  of  the  Eustachian  tubes  which  run  from  the  back  of 
the  nasal  passages  to  the  cavity.  This  action  should  be  repeated 
from  time  to  time  and  as  long  as  the  pressure  continues  to  in- 
crease. Relief  may  also  be  secured  by  the  action  of  swallowing. 
A  cold  makes  the  feat  more  difficult  since  the  Eustachian  tubes 
are  then  somewhat  blocked. 

Owing  to  breathing  the  denser  air  with  its  increased  amount  of 
oxygen,  as  soon  as  equilibrium  obtains  the  general  effect  is  some- 
what exhilarating  and  bracing.  To  quote  one  of  the  workmen  in 
the  Blackwall  tunnel  (England):  l"I  never  felt  happier  than 
when  I  was  in  the  compressed  air.  Always  happy,  and  on  the 
cheery  side.  Why,  laddie,  I  would  get  up  in  the  morning  feeling 
very  dour  and  queer,  and  just  go  into  the  workings  and  then 
whistle  (?)  and  sing  all  day  long." 

SENSATIONS  FELT  ON  LEAVING  AIR  CHAMBER. — On  leaving 
the  air  pressure  the  caissonier  feels  cold,  and  this  is  felt  most 
keenly  during  the  passage  through  the  air-lock,  being  due  to  the 
expansion  of  the  air  in  the  lock,  as  well  as  to  the  expansion  and 
liberation  of  gases  in  the  body.  To  counteract  the  effects  of 
this  cold  the  air-lock  shoulcf  be  warmed  and  the  men  given 
strong  hot  coffee  to  drink  on  emerging,  and  should  dress  warmly. 
Another  characteristic  of  decompression  is  a  dense  fog  which 
occurs  as  the  air  becomes  rarefied.  Another  sensation  often 
manifested  on  emerging  is  an  itching,  pricking  feeling  under  the 
skin  on  all  parts  of  the  body;  this  disappears  in  a  few  minutes. 
The  foregoing  are  the  sensations  always  felt;  if  the  person  is 
taken  with  caisson  illness  the  symptoms  may  be  manifold. 

l"  Coming  out  again  (from  the  working  pressure)  it  was  not  so  bad, 
but  just  chilly;  bitter  chilly,  cold  as  charity.  The  pains  would  come  on 
afterward,  in  an  hour  or  so,  or  when  you  got  into  bed.  Bends  in  the 

1  Engineering  News,  vol.  51,  page  437,  May  5,  1904. 


ART.  in    PHYSIOLOGICAL   EFFECTS   OF   COMPRESSED   AIR  331 

back,  the  wrists  and  the  legs;  just  awful.  Men  would  turn  out  in  the 
middle  of  the  night  and  come  back  to  the  works  and  get  into  the  compressed 
air  again  in  the  medical  locks.  They  had  a  full  dose  for  a  start,  and  let 
the  pressure  drop  gradually.  Then  they  went  back  home  to  bed.  Do 
them  any  good?  Eh,  mon,  its  no  for  me  to  say.  They  thought  so,  but 
I  thought  it  was  only  humbug,  a  faith  dodge.  When  I  had  bends  I  just 
jumped  about  and  took  a  drap  of  guid  whuskey — better  than  all  your 
doctor's  concoctions."  The  foregoing  graphic  description  of  the  'bends' 
and  treatment  for  it  indicates  the  attitude  of  the  average  'ground-hog.' 

114  The  symptoms  of  caisson  disease  have  been  quite  definitely  estab- 
lished. First  among  these  are  neuralgic  pains  of  an  intermittent  or 
paroxysmal  character,  and  of  varying  severity.  In  the  worst  instances 
these  pains,  or  cramps,  as  they  are  commonly  called — although  they  are 
rarely  accompanied  by  muscular  spasms — are  so  intense  as  to  completely 
unnerve  strong  men.  This  symptom  is  very  seldom  absent,  and  from  it 
comes  the  popular  name  of  'bends'  given  to  the  disease.  Another 
characteristic  symptom  which  is  always  exhibited  is  a  profuse  cold  per- 
spiration. Another  symptom  which  is  of  frequent  occurrence,  but  which 
is  not  always  exhibited,  is  pain  at  the  pit  of  the  stomach,  usually,  but  not 
always,  attended  by  vomiting.  In  about  50  percent  of  the  cases  observed, 
paralysis  has  been  a  characteristic  symptom.  The  degree  of  paralysis 
varies  from  slightly  impaired  sensation  or  numbness  in  the  extremities 
to  complete  loss  of  sensation  and  motion  in  the  affected  parts,  which  are 
most  frequently  the  legs  and  lower  part  of  the  body.  Finally  the  sufferer 
usually  exhibits  a  number  of  transient  symptoms,  which  have  their  origin 
in  the  brain;  these  are  headache,  dizziness,  double  vision,  incoherence  of 
speech,  and  sometimes  unconsciousness.  The  duration  of  these  symptoms 
varies  from  a  few  hours  to  several  weeks  in  case  of  paralysis.  In  fatal 
cases  congestion  of  the  brain  or  spinal  cord  always  exists.  A  very  notice- 
able fact  is  that  the  attack  of  the  disease  never  takes  place  while  the  sub- 
ject is  under  air  pressure,  but  always  occurs  while  he  is  emerging  from  the 
compressed  air  chamber  or  after  he  has  emerged." 

CAUSES  OF  CAISSON  DISEASE. — Various  theories  have  been 
advanced  from  time  to  time  relative  to  the  cause  of  caisson 
disease.  It  is  said  that  attention  was  first  called  to  caisson 
disease  at  about  the  middle  of  the  last  century  by  TRIGER  who 
applied  the  use  of  compressed  air  in  sinking  some  coal  shafts 
at  Chalons  on  the  banks  of  the  Loire.  2 "  HOPPE  SEYLER  (1857) 
and  THOMAS  SCHWANN  (1858)  in  Germany,  andBusQUOY  (1861) 

1  Engineering  News,  vol.  46,  page  157,  Sept.  5,  1901. 

2  Engineering  Record,  vol.  63,  page  362,  April  i,  1911. 


332  PNEUMATIC   CAISSONS   FOR  BRIDGES  CHAP.  IX 

in  France,  .  .  .  gave  the  first  correct  suggestion  as  to  the 
cause:  viz.,  that  it  was  due  to  the  setting  free  of  bubbles  of  gas 
in  the  blood.  Nitrogen  gas  is  dissolved,  according  to  the  law 
of  partial  pressures,  during  exposure  to  the  compressed  air,  and 
this  dissolved  gas  having  no  time  to  escape  through  the  lungs, 
if  the  pressure  be  suddenly  lowered,  bubbles  off  just  as  carbonic 
acid  escapes  from  aerated  water  when  a  bottle  is  uncorked." 

In  1871,  DR.  JAMINET,  the  physician  in  charge  of  the  com- 
pressed air  workers  at  the  St.  Louis  bridge,  became  convinced 
from  his  studies  that  the  disease  was  caused  by  too  rapid  a 
tissue  change  due  to  the  absorption  of  an  excess  of  oxygen. 

About  two  years  later,  DR.  A.  H. .  SMITH,  the  surgeon  in 
charge  of  the  New  York  tower  caisson  of  the  Brooklyn  bridge, 
arrived  at  the  conclusion  that  the  ill  effects  developed  in  work- 
ing under  compressed  air  were-due  to  the  pressure  of  the  air  forc- 
ing the  blood  from  the  surface  of  the  body  to  the  center  and 
thereby  causing  internal  congestion. 

But  it  was  PAUL  BERT,  who,  by  his  remarkable  experiments, 
published  in  1878,  proved  the  true  cause  of  caisson  disease  to  be 
the  effervescence  of  gas  in  the  blood  and  tissue  juices.  Since 
then  such  authorities  as  PHILLOPON,  VON  SCHROTTER,  HELLER, 
MAGER,  HALDANE,  HILL,  SMITH,  MACLEOD,  GREENWOOD  and 
others,  have  checked  and  extended  BERT'S  experiments. 

The  gas  which  is  present  in  the  blood,  and  which  comes  out 
of  solution  if  the  pressure  is  too  rapidly  lowered,  is  mostly 
nitrogen,  for  if  the  chamber  is  properly  ventilated  there  will 
be  only  a  small  amount  of  carbonic  acid  gas  in  the  air,  while 
the  oxygen  content  dissolved  by  the  blood  is  taken  up  chemically 
by  the  hemoglobin,  as  demonstrated  by  DR.  HALDANE.  As 
stated  elsewhere  the  tissue  fluids,  chiefly  the  blood,  dissolve  the 
air  according  to  D ALTON'S  law  of  solution  of  gases  in  fluids; 
i.e.,  the  amount  of  gas  dissolved  in  a  fluid  is  proportional  to  the 
pressure  of  the  gas  surrounding  the  fluid.  Except  for  very 
high  pressures,  such  as  eight  or  ten  atmospheres — values  which 
will  never  attain  in  caisson  work — these  dissolved  gases  probably 
have  no  chemical  effect  on  the  system,  and  are  quite  harmless 
as  long  as  they  remain  in  solution.  For  high  pressures  the  dis- 


ART.  112  PREVENTION   OF   CAISSON   DISEASE  333 

solved  oxygen  seems  to  have  a  toxic  effect,  causing  a  fatal 
inflammation  of  the  lungs.  Experiments  have  shown  that  with 
a  pressure  of  ten  atmospheres  some  animals  will  die  in  as  short 
a  time  as  20  minutes. 

However,  when  the  pressure  of  the  surrounding  air  is  lowered, 
the  dissolved  gases,  mostly  nitrogen,  are  thrown  out  of  solution 
in  the  form  of  bubbles.  If  the  lowering  of  the  pressure  is  done 
slowly  the  gases  are  thrown  out  of  the  blood  at  the  lungs  without 
developing  bubbles  of  any  appreciable  size.  But  if  the  pressure 
is  rapidly  lowered  the  gas  bubbles  stick,  owing  to  their  size, 
in  the  minute  blood  vessels  and  obstruct  the  flow  of  the  blood, 
often  causing  the  vessels  to  burst.  The  same  condition  ob- 
tains in  the  various  tissues  carrying  juices  saturated  with 
gas;  if  these  bubbles  develop  in  the  joints,  we  have  the 
'bends';  if  in  the  spinal  cord,  paralysis;  if  in  the  heart,  heart 
failure,  etc. 

ART.  112.     PREVENTION  or  CAISSON  DISEASE 

If  the  cause  of  caisson  illness  is  a  mechanical  action  due  to 
the  development  of  bubbles  in  the  blood  and  fluid  tissues,  which 
in  turn  is  due  to  too  rapid  decompression,  then  manifestly  the 
cure  is  decompression  at  a  rate  slow  enough  to  avoid  this  phe- 
nomenon. The  length  of  time  will  depend  upon  the  amount  of 
gas  in  the  fluid  tissues  and  upon  the  physical  characteristics  of 
the  person  being  decompressed.  The  amount  of  gas  in  the  fluid 
tissues  will,  in  turn,  depend  upon  (i)  the  degree  of  pressure  in 
the  working  chamber  and  (2)  the  length  of  time  under  pressure. 
The  length  of  time  taken  to  saturate  the  body  fluids  at  any 
particular  pressure  will  vary  greatly,  depending  upon  the  fat- 
ness of  the  subject,  the  amount  of  bodily  work  done,  heat  and 
moisture  present,  etc.  From  experiments  DR.  HALDANE  con- 
cluded that  in  certain  parts  of  the  body  where  the  circulation 
is  rapid  and  the  number  of  blood  vessels  high  the  tissue  juices 
will  become  50  percent  saturated  in  5  minutes,  with  complete 
saturation  in  40  minutes;  while  other  parts,  lacking  a  copious 
supply  of  blood,  will  require  75  minutes  for  50  percent  saturation 


334  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  IX 

and  about  4  hours  for  90  percent  saturation.  Experiments  show 
that  the  fatty  tissues  absorb  about  five  times  as  much  gas  as 
does  the  blood  and  the  rate  of  absorption  is  much  slower;  the 
rate  of  desaturation  will  be  correspondingly  slow.  For  this 
reason  men  inclined  toward  fatness  should  never  be  employed 
for  compressed-air  work.  The  better  the  circulation  of  the 
blood  the  more  quickly  and  easily  will  the  gases  be  thrown  out 
of  the  system;  for  this  reason  only  men  in  good  physical  condi- 
tion should  be  employed.  Old  men,  or  those  who  have  abused 
themselves  by  excessive  drinking  or  other  dissipation,  should 
never  be  allowed  in  the  working  chamber. 

Authorities  differ  as  to  the  time  that  should  be  allowed  for 
decompression,  but  all  agree  that  the  usual  time  given  is  too 
short.  Some  urge  a  uniform  rate  of  decompression,  while 
others  prefer  stage  decompression,  that  is,  at  first  a  rapid  decom- 
pression to  a  certain  pressure,  followed  by  slower  decompression. 

Seldom  is  more  than  15  or  1 8  minutes  given  to  decompression; 
the  reason  for  this  is  that  the  air-lock  is  small  and  as  a  conse- 
quence the  men  must  maintain  cramped  positions  in  the  same. 
Moreover,  the  lock  is  usually  cold  and  filled  with  fog,  due  to 
the  decreasing  pressure.  Properly,  the  lock  should  be  large 
enough  to  allow  the  men  some  freedom  of  motion  and  it  should 
be  ventilated  with  warm  dry  air.  The  French  law,  enacted  in 
1908,  prescribes  that  for  a  head  of  water  up  to  65.6  feet  not  less 
than  21.2  cubic  feet  of  air  shall  be  provided  for  each  man  in  the 
lock,  and  for  depths  above  this  not  less  than  24.7  cubic  feet. 
During  decompression  the  men  should  constantly  move  about 
and  massage  their  various  joints,  as  this  has  been  found  to  assist 
materially  in  ridding  the  system  of  the  gases. 

MACLEOD  suggests  the  following  time  for  decompression  as 
being  safe: 

Gage  Pressure  Length  of  Shift  Decompression  Period 

15  to  30  4  hours  |  to  i  hour 

45  to  60  4  hours  i^  to  2  hours 

In  Germany,  VON  SCHROTTER,  HELLER  and  MAGER,  in  1900, 
published  a  work  in  which  they  laid  down  the  principle  that  a 


ART.  112 


PREVENTION   OF    CAISSON   DISEASE 


335 


uniform  decompression  at  the  rate  of  two  minutes  per  o.i  atmos- 
phere, or  20  minutes  per  atmosphere,  was  safe. 

The  law  of  New  York  State  (1913)  governing  the  time  of 
decompression  for  pneumatic  caisson  work  for  bridges  and  build- 
ings is  as  follows: 

Gage  pressure  in  pounds  10     15     20     25     30    36    40     50 

Time  of  decompression  in  minutes        i       2       5      10     12     15     20     25 

The  time  of  work  in  caissons,  given  by  this  law,  is  as  follows : 


Gage  pressure- 

0-21 

22-30 

31-35 

36-40 

4i-4S 

45-so 

Time  per  day  in 

8  hrs. 

6  hrs. 

4  hrs. 

3  hrs. 

2  hrs. 

i*  hrs. 

caisson. 

No.  of  shifts. 

2  (minimum) 

2 

2 

2  (min  ) 

Length  of  shift.  .  .  . 

•3  hrs 

2  hrs 

ji  hrs 

i  hr 

§  hr 

(max.) 

(max.) 

Minimum  time  be- 

30 consecutive 

i  hr. 

2  hrs. 

3  hrs. 

4  hrs. 

5  hrs. 

tween  shifts. 

minutes 

The  theory  upon  which  stage  compression  is  based  is  that  the 
gas  in  the  blood  will  not  effervesce  until  a  marked  diminution  of 
pressure  obtains,  and  as,  to  the  point  of  effervescence,  the  gases 
are  discharged  at  a  rate  varying  with  some  function  of  the 
change  of  pressure,  manifestly  the  more  rapid  the  lowering  of 
pressure  the  more  quickly  will  the  blood  vessels  be  freed  of  the 
gases  contained  therein.  Since  almost  no  cases  of  aeremia  are 
caused  by  rapid  decompression  from  about  19  pounds  gage  pres- 
sure, it  seems  reasonable  to  assume  that  the  pressure  in  the  air- 
lock may  be  reduced  that  amount  in  about  three  minutes;  from 
this  point  the  pressure  must  be  lowered  quite  slowly  and  should 
correspond  to  the  natural  rate  of  desaturation  of  the  fluid 
tissues  at  that  difference  of  pressure.  When  the  gage  pressure 
reaches  about  19  pounds,  the  remainder  of  the  decompression 
may  be  done  quickly,  for,  as  stated  above,  it  appears  that  the 
average  person  can  safely  stand  that  difference  of  pressure.  The 
fundamental  idea  upon  which  stage  decompression  is  based  is 
correct,  but  as  there  is  but  little  experimental  data  and  less 
precedent  to  guide  one,  it  has  not  yet  become  general. 

Apart  from  the  matter  of  slow  decompression,  other  precau- 


336  PNEUMATIC   CAISSONS  FOR  BRIDGES  CHAP.  IX 

tions,  if  taken,  will  do  much  to  lessen  the  occurrence  of  caisson 
disease.  Anything  which  tends  to  lower  the  vital  resistance  of 
the  human  system  tends  to  promote  caisson  illness.  For  this 
reason  the  physical  conditions  under  which  the  men  work  should 
be  as  good  as  it 'is  possible  to  make  them:  There  should  be 
furnished  plenty  of  fresh  air;  electric  lighting  rather  than  gas  or 
candle  lighting  should  always  be  employed,  as  the  latter  tends 
to  vitiate  the  air;  the  air  should  be  kept  at  as  reasonable  a 
temperature  as  possible,  which  means  that  it  should  be  cooled 
during  the  summer  time,  as  compression  raises  its  temperature. 
At  present  this  is  done  in  practically  all  work,  either  by  spraying 
the  compressed  air  as  it  enters  the  working  chamber,  or  else  by 
passing  it  through  a  coil  of  pipes  externally  cooled. 

J"It  is  well  known  that,  in  a  confined  atmosphere,  man 
sooner  or  later  suffers  from  the  accumulation  of  poisonous 
gases.  The  criterion  of  this  pollution  of  the  atmosphere  is  the 
amount  of  carbonic  acid  (CO2)  found  present.  When  the  per- 
centage of  CO2  in  the  air  rises  above  o.i  percent,  evil  effects  are 
common.  It  should  be  clearly  understood  that  these  evil 
effects  are  not  due  to  the  carbonic  acid  itself,  but  to  some  other 
toxic  property  which  the  CC>2  content  seems  to  run  parallel 
with,  and  is,  therefore,  a  measure  of  it.  Now  under  pressure 
it  is  evident  that  such  a  gas  will  be  still  more  dangerous.  As  a 
matter  of  fact,  E.  H.  SNELL  reports  that  an  'increase  of  CO2 
from  0.04  percent  to  o.i  percent  at  30  pounds  pressure  is  the 
forerunner  of  much  illness.'  He  found  that  by  free  ventilation 
of  the  caisson,  so  as  to  remove  this  CO2,  the  illness  dropped  from 
seven  cases  a  day  to  one  case  in  two  days.  .  .  .  Ventilation  is  a 
matter  which  should  be  carefully  provided  for,  since  otherwise 
the  COz  and  other  poisonous  constituents  of  polluted  air  will 
have  their  usual  depressing  effects  on  the  workmen  and  render 
them  more  prone  to  suffer  from  decompression  symptoms." 

Especially  when  sinking  through  foul  material  should  care  be 
exercised  in  keeping  the  air  pure.  T  K.  THOMSON  reports  that 
when  sinking  through  the  foul  bottom  of  the  Harlem  River  the 

1  Cause,  Treatment  and  Prevention  of  the  Bends,  by  J.  J.  R.  MACLEOD, 
Journ.  Assoc.  Eng.  Soc.,  vol.  39,  page  301,  Nov.,  1907. 


ART.  ii2  PREVENTION   OF   CAISSON  DISEASE  337 

men  suffered  much  from  the  bends,  but  when  sinking  through 
the  clay  below  this,  even  though  under  a  much  greater  pressure, 
very  little  trouble  occurred.  It  is  also  noticed  that  a  greater 
amount  of  sickness  is  apt  to  occur  during  concreting  than  at 
other  times,  this  being  due  to  the  decrease  in  the  leakage  of 
the  air,  or  inadequate  ventilation. 

CURE  FOR  CAISSON  DISEASE. — The  best  and  about  the  only 
cure  for  caisson  disease  is  recompression  with  slow  decompres- 
sion. If  the  patient  can  be  put  into  the  air  before  the  gas  bub- 
bles have  had  a  chance  to  tear  the  blood  vessels  and  fluid  tissues 
a  cure  can  usually  be  effected,  but  otherwise  not.  For  this 
reason,  a  hospital  air-lock,  large  and  well  ventilated,  should 
always  be  maintained  in  readiness  and  the  men  should  be 
housed  near  by,  so  that  in  case  of  delayed  attacks  they  may 
be  immediately  recompressed. 


CHAPTER  X 

PNEUMATIC  CAISSONS  FOR  BUILDINGS 

ART.  113.     GENERAL  DEVELOPMENT 

The  application  of  the  pneumatic  caisson  to  building  founda- 
tions has  been  restricted  very  largely  to  the  tall  buildings  or 
'  skyscrapers'  of  New  York  City.  Two  conditions  occur  there 
which  require  this  form  of  foundation:  First,  the  necessity  for 
carrying  the  column  loads  to  bedrock;  and  second,  the  presence 
of  quicksand  over  the  rock.  Both  the  height  of  the  buildings 
and  the  magnitude  of  the  column  loads  make  it  imperative  to 
found  the  piers  on  a  very  hard  and  unyielding  stratum,  prefer- 
ably bedrock,  since  any  irregular  settlement  is  exceedingly 
dangerous  and  difficult  to  remedy  in  tall  buildings.  The  pres- 
ence of  quicksand  makes  sinking  to  bedrock  very  difficult  by 
other  methods  than  that  of  the  pneumatic  caisson,  due  to  the 
tendency  of  the  material  to  flow  into  the  excavation;  while  it  is 
especially  dangerous  in  the  lower  part  of  Manhattan  Island, 
due  to  the  liability  of  undermining  adjacent  building  founda- 
tions, many  of  which  rest  on  shallow  foundations.  The  only 
disadvantage  of  the  pneumatic  method  is  its  high  cost,  but 
this  is  fully  justified  where  the  security  of  very  expensive 
buildings  is  at  stake. 

In  its  details,  the  caisson  for  a  building  does  not  differ  mate- 
rially, except  in  the  matter  of  size,  from  the  bridge  caisson.  It 
is  customary  in  most  cases  to  use  separate  piers  for  all  the  inte- 
rior columns,  these  being  circular  or  square  in  plan;  but  special 
conditions,  such  as  the  close  spacing  of  two  or  more  columns,  or 
lack  of  clearance,  sometimes  makes  it  necessary  to  use  one  pier 
for  two  or  more  columns.  Where  the  grade  of  the  cellar  floor 
is  below  the  ground-water  line  the  wall  piers  often  serve  two 
functions:  First,  that  of  carrying  the  wall- column  loads  to  rock; 

338 


ART.  113  GENERAL  DEVELOPMENT  339 

and  second,  that  of  acting  as  a  dam  or  retaining  wall  to  keep  out 
the  water.  To  accomplish  the  latter  they  must  form  a  continu- 
ous wall  and  hence  they  are  made  rectangular  in  plan,  as  wide 
as  is  necessary  to  give  the  required  stability  as  a  dam  or  retain- 
ing wall — usually  between  6  and  8  feet — and  as  long  as 
can  be  conveniently  handled,  which  is  often  as  much  as  30 
feet.  The  ends  of  adjacent  sections  are  then  connected  and 
made  water-tight. 

For  the  circular  form  of  caisson  the  diameter  may  vary  from 
about  6  feet  as  a  minimum  to  15  feet  or  more.  For  a  rectangu- 
lar section  the  largest  that  has  ever  been  used  for  building  foun- 
dations is  in  the  New  York  Telephone  Co.  Building,  where  the 
largest  caissons  are  35  feet  3  inches  by  38  feet  8  inches  in  plan. 
But  more  remarkable  in  many  respects  were  some  of  the  caissons 
used  in  the  foundations  of  the  Municipal  Building,  New  York, 
one  of  which  was  26  X  31  feet,  and  carried  the  load  from  five 
columns.  In  size  this  is  not  much  larger  than  one  used  in  the 
first  building  founded  on  pneumatic  caissons;  namely,  the 
Manhattan  Life  Insurance  Building,  erected  in  1893-94,  where 
the  caissons  had  dimensions  of  21  feet  6  inches  by  25  feet  6 
inches.  But  in  the  magnitude  of  the  single  column  loads  and 
depth  to  which  the  caisson  was  sunk,  a  great  development  is 
apparent.  The  maximum  column  load  in  the  Manhattan  Life 
Building  was  about  400  ooo  pounds,  while  in  the  Municipal 
Building  it  was  about  5  475  ooo  pounds;  the  depth  of  sinking 
below  the  street  curb  in  the  former  was  54  feet,  while  in  the  lat- 
ter it  was  140  feet;  the  maximum  air  pressures  (gage)  used 
were  respectively  15  and  48  pounds  per  square  inch,  the  latter 
being  within  2  pounds  of  the  maximum  allowed  by  State  law. 
The  140-foot  depth  below  the  curb  corresponded  to  a  depth  of 
about  112  feet  below  the  level  of  general  excavation.  For  the 
most  part  the  depth  to  which  pneumatic  caissons  for  buildings 
have  been  sunk  have  ranged  somewhere  between  30  and  90  feet 
below  the  curb,  the  true  depth  of  sinking  and  the  hydrostatic 
head  worked  against  being  less  than  this,  depending  on  the 
amount  of  general  excavating  done  before  sinking  the  caissons 
and  the  position  of  the  ground-water  level,  respectively. 


340  PNEUMATIC   CAISSONS   FOR  BUILDINGS  CHAP.  X 

In  the  development  of  pneumatic  caissons  for  building 
foundations  a  tendency  was  manifested  early  to  do  away  with 
permanent  shafts  and  roofs  of  the  working  chambers  by  making 
them  removable.  When  present  as  a  permanent  part  of  the 
pier  they  tend  to  divide  the  pier  into  two  separate  monoliths  of 
concrete,  one  an  inverted  T-shaped  mass  formed  by  the  filling 
in  the  working  chamber  and  shaft  well  and  the  other  a  ring- 
shaped  mass  surrounding  the  shaft.  Removing  the  shaft 
before  filling  the  well  with  concrete  has  now  become  standard 
practice,  while  the  use  of  a  temporary  roof  is  very  general.  The 
two  common  methods  of  accomplishing  the  latter  are*  First,  to 
fill  the  crib  with  concrete  only  after  the  caisson  is  sunk  and  the 
roof  removed;  and  second,  to  use  a  roof  of  reinforced  concrete. 

Pneumatic  caissons  made  of  wood,  steel,  wood  and  steel 
combined,  and  of  reinforced  concrete  have  been  used.  They  are 
all  satisfactory  and  the  choice  in  any  particular  case  will  depend 
on  current  prices  and  the  time  required  to  obtain  the  materials 
and  to  construct  the  caisson.  As  a  rule  in  this  country  concrete 
is  the  most  economical  and  steel  the  most  expensive,  and  wood 
about  half-way  between. 

ART.  114.     CAISSONS  OF  TIMBER 

Caissons  made  entirely  of  wood  have  been  and  are  being 
extensively  used,  although  not  to  the  same  extent  that  they  are 
employed  for  bridge  caissons.  For  square  and  rectangu- 
lar caissons  the  construction  is  simple  and  the  time  there- 
fore saved  as  compared  with  those  of  steel  or  concrete,  may  be 
considerable. 

Where  the  depth  is  not  great  nor  the  sinking  difficult,  the 
caisson  and  crib  may  be  made  of  light  construction.  Such  a 
form  is  exemplified  in  the  caissons  of  the  Rogers  Building, 
New  York,  which  varied  in  dimensions  from  8  feet  square  to 
about  7X14  feet  in  plan,  and  were  sunk  to  depths  of  from 
28Lto  60  feet  below  the  curb,  corresponding  to  about  35  to  40 
feet  below  the  excavation  level.  The  sides  were  made  of  3-inch 
vertical  plank  fastened  to  two  horizontal  rectangular  frames,  one 


ART.  114 


CAISSONS    OF    TIMBER 


341 


near  the  bottom  and  the  other  about  3  feet  higher,  and  to  the 
roof  timbers,  by  two  f-inch  bolts  at  every  intersection,  the 
bolt  heads  being  countersunk  into  the  planks  on  the  outside. 
All  joints  were  caulked  on  the  outside  with  oakum.  The  cutting 


K- 

ENO.NEWS. 


•  24' 0" - 

Half  Deck  Plan.  Half  Plan  of  Working  Chamber. 

FIG.   1140. — Pneumatic  Caisson  of  Timber  Construction. 


edge  was  made  by  beveling  the  inside  lower  ends  of  the  planking 
to  a  thickness  of  i  inch.  The  lower  horizontal  which  was  of 
4X1 2-inch  material  was  but  a  few  inches  above  the  cutting 
edge  and  hence  reinforced  the  same.  The  working  chamber  had 
a  clear  height  of  6  feet  and  was  covered  with  a  roof  made  of  two 


342  PNEUMATIC   CAISSONS   FOR  BUILDINGS  CHAP.  X 

solid  courses  of  crossed  8  X  8-inch  timber,  the  lower  course  rest- 
ing on  6  X  8-inch  timbers  bolted  to  the  sheathing. 

The  sheathing  projected  6  feet  above  the  lower  side  of  the 
roof  of  the  working  chamber  and  formed  one  section  of  the  crib 
The  other  sections  were  made  in  1 4-foot  lengths  and  were 
of  the  same  general  construction  as  the  caisson  sides.  At  the 
joints  between  the  successive  sections  of  the  crib  the  ends  of  the 
sheathing  were  cut  square  and  braced  by  an  inside  6  X 1 2-inch 
frame,  the  latter  being  bolted  to  both  sections  to  serve  as  a 
connecting  flange.  The  cribs  were  braced  at  intermediate 
points  by  6  X  8-inch  horizontal  timber  frames. 

A  much  stronger  form  of  wooden  pneumatic  caisson  is  illus- 
trated in  Fig.  1 14  a,  which  is  one  of  the  1 2  X  24-foot  caissons  used 
in  the  Gillender  Building  foundations.  The  sides  of  the  work- 
ing chamber  were  composed  of  two  thicknesses  of  12X1 2-inch 
timbers  sheathed  on  the  outside  and  inside  with  3! -inch  mate- 
rial. The  cutting-edge  timber  extended  out  beyond  the  walls, 
the  outer  part  of  the  upper  side  abutting  against  the  bottom  of 
the  outside  sheathing,  while  the  outside  and  bottom  faces  were 
protected  by  the  cutting  edge,  which  consisted  of  a  steel  angle 
and  a  vertical  steel  plate. 

The  roof  consisted  of  three  thicknesses  of  12X1 2-inch  timbers, 
the  upper  and  lower  ones  running  transversely  and  the  inter- 
mediate one  longitudinally.  The  under  side  of  the  roof  was- 
sheathed  with  3! -inch  material.  The  crib  was  composed  of  31- 
inch  sheathing,  braced  at  intervals  by  horizontal  frames  of 
8X i2-inch  timbers. 

If  less  strength  is  desired  the  walls  may  be  made  of  a  single 
thickness  of  horizontal  timbers  laid  closely  and  sheathed  on  the 
outside  and  inside.  This  was  done  in  the  caissons  for  the 
Mercantile  Building,  the  timbers  being  6X10  inches,  the  latter 
dimension  horizontal,  while  the  sheathing  consisted  of  3  X  12- 
inch  planks.  In  this  case  the  roof  was  composed  of  a  double 
thickness  of  1 2-inch  timbers. 

The  foregoing  examples  have  permanent  roof  construction. 
The  first  wooden  caissons  doing  away  with  this  feature  were 
those  of  the  United  States  Express  Co.  Building.  Here  the  wall 


ART.  114 


CAISSONS    OF   TIMBER 


343 


caissons  were  built  with  a  width  of  5!  feet,  a  height  of  6  feet, 
and  with  lengths  varying  from  25  to  34  feet.  The  walls  con- 
sisted of  a  single  thickness  of  timber  varying  from  6X12 
inches  to  10X12  inches.  Across  the  ioXio-inch  top  course 
were  placed  3X3Xj-inch  angles  running  transversely  and 
spaced  3  feet  apart,  the  vertical  flanges  being  turned  up.  On 
these  was  placed  a  layer  of  if -inch  tongue  and  groove  boards 
which  served  as  a  form  for  concrete  placed  on  top  of  the  same. 

Instead  of  a  crib,  molds  built  of  vertical  tongue-and-grooved 
boards  in  sections  8  feet  high,  having  the  same  length  and 
breadth  as  the  caisson,  were  built  on  top  of  the  latter  to  receive 
the  concrete.  They  were  held  together  by  outside  horizontal. 


Type  A. 

Steel  Working  Chamber 

for  small  circular  Caissons 

;(6'6"to8'6"Diam.) 


Type  B.  '  Type's  C&D 

Timber  Working  Chamberfor  Concrete  Working  Chamber  for  large 

Small  rectangular  Caissons  ,    circular  &  rectangular  Caissons. 

(5'6"to  7'6'wide.)  (Circular  9'tol4'2";rectangular  8'wideandover.)l 

FIG.  1146. — Types  of  Working  Chambers,  Municipal  Building,  New  York. 


yokes,  each  made  with  4X3X|-inch  angles  forming  a  rectangu- 
lar frame.  Three  yokes  were  used  to  a  section,  one  at  the  top, 
one  at  the  middle,  and  one  at  the  bottom.  On  completion  of 
the  forms,  a  six-inch  layer  of  concrete  was  placed  on  the  roof 
forms;  as  soon  as  this  had  hardened  somewhat  2  feet  more 
of  concrete  was  added,  and  this  2^-foot  thickness  of  concrete 
served  as  the  permanent  roof,  the  temporary  panels  underneath 
being  taken  off. 

Fig.  1 146,  type  B,  shows  the  type  used  in  the  Municipal  Build- 
ing for  rectangular  caissons  5!  to  y|  feet  wide.  It  closely  resem- 
bles those  described  in  the  two  preceding  paragraphs,  the  walls 
being  made  of  a  single  thickness  of  i2Xi2-inch  and  8X1 2-inch 
timbers,  the  bottom  timbers  being  faced  with  4X4-mcn  steel 
angles  to  form  the  cutting  edge.  It  was  provided  with  a  tempo- 


344 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


rary  deck  of  2 -inch  planks  notched  into  the  walls  and  this  deck 
was  removed  after  the  first  layer  of  roof  concrete  had  hardened. 
The  approximately  square  caissons  used  in  the  foundations  of 
the  Adams  Express  Building,  New  York,  are  illustrated  in  Fig. 
1 14  c.  The  working  chamber  was  6  feet  high  and  had  sides  com- 
posed of  4X1 2-inch  timbers  dressed  on  all  sides  and  caulked. 
These  sides  were  braced  with  vertical  inside  i2Xi2-inch 


\>—9'6"Cassion  */5— 
Side  Elevation  Elevation  B~B 

FIG.   ii4c. — Caissons,  Adams  Express  Bldg.,  New  York. 

timbers  at  the  four  corners  and  at  the  mid-lengths,  the  latter 
extending  beyond  the  caisson.  The  outside  was  sheathed  with 
2  X  8-inch  vertical  tongue-and-grooved  planks,  which  extended 
up  beyond  the  caisson  to  serve  as  a  form  for  the  concrete  above 
the  caisson.  This  sheathing  took  bearing  against  horizontal 
12 X  i2-inch  timbers  spaced  4  feet  apart  vertically,  and  arranged 
in  pairs  at  right  angles  to  each  other,  each  pair  being  connected 


ART.  115 


CAISSONS    WITH   METAL    SHELLS 


345 


Q'O"       — - 


together  with  screw-ended  rods.  The  sides  were  held  apart  by 
3  X  8-inch  struts  which  were  removed  when  the  concrete  had 
been  placed. 

The  cutting-edge  timber  was  6X12  inches  in  section,  beveled 
on  the  inner  corner  and  projected  beyond  the  horizontal  timbers 
to  cover  the  lower  ends  of  the 
outside  sheathing.     The  top  of 
the     working     chamber     was 
covered  with  4X1 2-inch  hori- 
zontal boards  to  serve  as  a  form 
for  the  concrete  above. 

A  3-foot  layer  of  1-2-4  con~ 
crete  was  first  placed  on  the 
deck,  allowed  to  harden  for  24 
hours,  after  which  a  6-foot  layer 
was  added  every  24  hours. 
The  deck  sheathing  was  re- 
moved 48  hours  after  the  first 
layer  of  concrete  was  placed. 


Plan. 


ART.  115.     CAISSONS  WITH 
METAL  SHELLS 


/  Connection  for  Cofferdam. 


Working 


8)3   W"*&**lf 


Chamber. 


(^uwing 
Sectional 


Elevation. 


The  use  of  steel  shells  for 
small  circular  pneumatic  cais- 
sons has  become  standard  prac- 
tice, but  their  use  for  caissons 
of  a  square  or  rectangular  shape 
is  rapidly  decreasing.  The  ad- 
vantages of  the  steel  shell  may 
be  summarized  as  follows:  First, 
the  thickness  of  the  shell  being  small  there  is  a  maximum 
amount  of  working  space  in  the  air  chamber,  as  well  as  a 
maximum  amount  of  space  to  be  filled  with  concrete;  second, 
for  the  cylindrical  form  it  compares  favorably  in  ease  of  con- 
struction with  wood  and  concrete;  and  third,  it  is  easily  made 
water-tight. 


FIG.  11501 — Caisson  for  Inside  Col- 
umn. Foundation,  Mutual  Life  Bldg., 
New  York. 


346 


PNEUMATIC   CAISSONS  FOR  BUILDINGS 


CHAP.  X 


The  first  pneumatic  caissons  used  for  a  building,  those  of 
the  Manhattan  Life  Building,  were  made  of  steel,  and  were  both 
circular  and  rectangular  in  section.  Figs.  115^  and  b  show  the 
details  of  both  forms  of  caissons  used  in  the  foundations  of  the 
Mutual  Life  Building.  The  caissons  were  sunk  to  solid  rock, 


Connection  for  Air  Shaft  v 


Connection  for  Air  Lock 


Sectional 
Cofferdam   Connection  Angle.  \ 


Plan. 

Cofi&rdam  'Connection  An 

fl 


|« ._    9>0' > 

Half  Longitudinal  Sectional    Elevation. 
Inoide. 


^  Half  End 
Elevotior 
Outside. 


Cuffing  Edge. 

8'0"     

Half  Transverse 
Sectional  Elevation. 


FIG.   1156. — Caisson  for  Wall  Column.     Mutual  Life  Bldg.,  New  York. 

from  70  to  90  feet  below  the  curb  and  from  50  to  70  feet  below 
ground-water  level.  The  roof  of  the  cylindrical  caisson  was 
made  of  TV-inch  steel  plates  riveted  to  the  lower  flanges  of  15- 
inch  I-beams,  as  well  as  to  the  shell  of  the  caisson.  The  latter 
consisted  of  f -inch  steel  plates  braced  at  intervals  with  circular 
4X4Xj-inch  steel  angles.  The  lower  part  of  the  shell,  rein- 
forced with  an  iSXf-inch  plate,  formed  the  cutting  edge.  In 


FIG.   use. — Sinking    and    Concreting    Caissons,    with    Steel    Forms.     Municipal 

Building  (Facing  p.  346.) 


348 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


those  shapes  of  structural  steel  were  used 
that  could  readily  be  obtained  in  the  open 
market;  the  rest  of  the  structure  was  made 
of  wood,  and  the  two  materials  combined 
in  the  simplest  possible  manner. 

For  circular  piers  the  caisson  has  a  diam- 
eter varying  from  6  to  12  feet;  for  diameters 
less  than  6  feet  it  is  a  difficult  matter  to 
excavate  the  material  in  the  working  cham- 
ber, and  on  the  other  hand,  few  single 
column  loads  are  large  enough  to  require 
a  caisson  with  a  diameter  of  over  12  feet. 
The  circular  caisson  is  made  of  staves 
about  4X6  inches  in  section,  usually  dressed 
down  to  somewhat  smaller  dimensions,  the 
outer  and  inner  surfaces  being  cylindrical. 
The  staves  are  fastened,  at  every  intersec- 
tion, to  inside  3  X 3-inch  horizontal  angle- 
iron  rings,  spaced  from  3  to  5  feet  apart, 
bolts  of  about  f  inch  in  diameter  and  coun- 
tersunk into  the  wood  being  used  for  this 
purpose.  The  staves  are  usually  splined 
but  in  some  cases  they  are  only  caulked. 
This  type  is  illustrated  in  Fig.  n6a. 

In  the  circular  caissons  of  the  Atlantic 
Mutual  Building,  which  had  an  average 
diameter  of  about  7  feet,  the  cutting  edges 
were  made  with  a  28Xf-inch  steel  plate. 
To  give  bearing  surface  to  the  cutting  edge, 
in  order  to  better  control  the  sinking  and  to 
protect  the  feet  of  the  staves,  a  3X3Xf- 
inch  angle  was  riveted  to  the  inside  of  the 
plate,  parallel  to  its  bottom  edge,  and  J 
inch  above  it,  the  horizontal  leg  forming  a 
shelf  to  receive  the  lower  ends  of  the  staves. 
FIG.  ii 6a.— Wooden  The  roof  of  the  working  chamber  was  formed 

Stave  Caisson  with  De-     , 

tachabie  Roof  and  shaft    by  a  removable  steel   dome  |  inch  thick, 


ART.  117  CAISSONS   OF   REINFORCED   CONCRETE  349 

made  in  two  sections  and  stiffened  with  radial  steel  angles.  It 
was  caulked  with  a  hemp  gasket  and  bolted  to  a  3  X 3-inch  in- 
side steel  angle  ring  about  6|  feet  above  the  cutting  edge. 

The  crib  was  of  the  same  form  of  construction  as  the  caisson, 
and  was  built  as  a  continuation  of  the  same  to  a  height  of  32 
feet  above  the  cutting  edge.  Where  the  32  feet  was  not 
sufficient  in  height  short  lengths  were  added  on  top.  These 
were  made  in  two  semi-cylindrical  sections  and  were  butt- 
jointed  to  the  top  of  the  crib  already  in  place,  and  were  caulked 
and  bolted  through  the  horizontal  flanges  of  the  angle-iron  rings. 

For  the  wall  piers  of  the  New  York  Stock  Exchange  Building 
the  caissons  were  made  rectangular  in  form,  8  feet  wide,  from 
24  to  30  feet  long,  and  8  feet  high.  They  were  sheathed  with 
4X1 2-inch  vertical  wooden  staves  with  square  caulked  edges 
and  without  splines.  These  staves  were  fastened  to  successive 
courses  of  inside  horizontal  steel  angles,  the  latter  extending 
wholly  around  the  caisson.  The  longitudinal  walls  were  braced 
with  horizontal  transverse  timbers  resting  on  and  bolted  to  the 
angle  frames,  as  well  as  with  tie  rods,  parallel  and  adjacent  to 
the  timber  braces.  The  roof  was  formed  with  a  removable 
steel  plate  dome,  reinforced  with  transverse  angles  and  fastened 
to  frame  angles  about  6  feet  above  the  cutting  edge. 

The  crib  was  exactly  like  the  caisson,  except  that  it  was  with- 
out roof  or  cutting  edge.  It  was  built  in  sections  15  feet  high. 
The  angle  frames  at  the  top  of  each  section  were  set  3  inches 
below  the  top  of  the  staves  with  the  horizontal  flange  up.  The 
angle  at  the  bottom  of  the  next  upper  section  had  its  horizontal 
flange  down  and  i  inch  below  the  lower  end  of  the  staves.  This 
engaged  the  lower  section  and  formed  a  tenon,  thus  binding  the 
two  sections  together.  A  row  of  eye  bolts,  i  foot  apart,  con- 
nected the  horizontal  flanges  of  the  angle  frames. 

ART.  117.     CAISSONS  OF  REINFORCED  CONCRETE 

Pneumatic  caissons  of  reinforced  concrete  are  now  being 
widely  used.  The  chief  advantage  of  this  type  of  caisson  is 
that  it  gives  a  monolithic  pier.  A  second  advantage  is  that  the 
caisson  may  be  made  at  the  site,  thus  avoiding  the  expense  of 


350  PNEUMATIC   CAISSONS  FOR  BUILDINGS  CHAP.  X 

teaming  the  same.  One  disadvantage  is  that  the  required  thick- 
ness of  walls  so  reduces  the  working  space  that  this  type  cannot 
be  used  for  very  small  caissons.  Another  disadvantage  is  the 
time  element  involved  in  waiting  for  the  concrete  shell  to  harden. 

The  foundation  caissons  of  the  Municipal  Building  were 
sunk  in  1910  and  were  the  first  in  which  reinforced  concrete 
was  used  throughout.  Here  both  the  circular  and  rectangular 
forms  were  employed;  all  circular  caissons  having  diameters  9 
feet  or  over  and  all  rectangular  ones  having  a  width  of  8  feet  or 
over,  were  made  of  reinforced  concrete.  Types  C  and  D,  Fig. 
114  b,  show  the  outlines  of  the  caissons;  it  will  be  noticed  that  the 
walls  thicken  from  the  cutting  edge  to  the  roof  by  stepping  the 
concrete.  As  noted  in  Art.  94,  this  is  a  better  arrangement 
than  the  tapered  form  because  it  gives  a  positive  bearing 
between  the  chamber  shell  and  the  concrete  filling,  thus  making 
the  whole  area  of  the  bottom  available  for  carrying  the  load, 
without  relying  on  any  bond  stress.  The  thickness  of  the  bot- 
tom of  the  wall  was  about  10  inches  and  the  real  cutting  edge 
consisted  of  a  steel  channel  and  a  4  X 4-inch  steel  angle,  the 
former  laid  horizontally  with  flanges  up  and  the  latter  with  its 
vertical  leg  down,  thus  giving  the  sharp  cutting  edge  and  broad 
bearing  surface.  The  walls  were  well  reinforced  with  both 
vertical  and  horizontal  rods. 

No  cribs  were  used,  simple  forms  being  employed  in  which 
to  build  a  concrete  shell,  which  was  constructed  before  sinking 
was  started.  The  caisson  and  the  shell  above  the  same  were 
built  directly  on  the  spot  where  they  were  to  be  sunk.  The 
forms  for  the  interior  of  both  circular  and  rectangular  caissons 
were  made  of  wood,  while  for  the  exterior  faces  and  for  the  shell 
above  the  roof  they  were  made  of  steel  for  the  circular  ones,  and 
of  wood  for  the  rectangular  ones.  In  the  reinforced-concrete 
foundations  for  the  Woolworth  Building,  New  York,  the  inner 
forms  were  also  of  steel  for  the  circular  caissons. 

ART.  118.     CRIB  AND  COFFERDAM 

The  frame  which  is  built  on  top  of  the  caisson  and  which, 
together  with  the  roof  of  the  caisson,  virtually  forms  an  open 


ART.  118  CRIB   AND   COFFERDAM  351 

box  caisson,  is  generally  called  a  cofferdam  when  applied  to  cais- 
son construction  for  buildings.  In  the  preceding  articles,  it 
was  designated  as  a  crib,  since  it  corresponds  to  the  crib  of  the 
bridge  substructure.  This  frame  is  usually  built  in  sections,  as 
noted  in  the  preceding  pages,  and  the  top  section  sometimes 
forms  a  true  cofferdam.  As  water  seldom  covers  the  ground  for 
such  caissons  the  cofferdam  is  not  often  employed,  about  the 
only  time  when  it  is  used,  is  when  the  caisson  is  sunk  before 
the  general  excavation  for  the  cellar  or  sub-surface  floors  is 
made.  In  the  latter  case  the  cofferdam  serves  as  a  form  just 
as  the  crib  proper  does,  but  after  the  general  excavation  is 
completed  the  cofferdam  is  removed. 

In  the  early  deep  foundations,  such  as  those  of  the  Manhattan 
Life  Building,  brick  masonry  was  used  for  the  pier  material  above 
the  caisson,  in  which  case  the  use  of  cribs  was  ordinarily  dis- 
pensed with,  the  masonry  being  built  up  as  the  caisson  sank. 
But  this  arrangement  was  not  entirely  satisfactory  for  it  was 
found  that  in  omitting  the  crib  the  friction  on  the  sides  was  much 
increased,  which  was  a  disadvantage  in  itself,  and  especially 
dangerous  in  that  it  tended  to  tear  apart  the  brick  masonry. 
Another  desirable  feature  of  the  crib  is  that  it  enables  sinking  to 
be  carried  on  without  regard  to  the  progress  of  the  masonry 
construction. 

When  brick  masonry  was  superseded  by  concrete,  the  latter 
being  deposited  on  the  deck  of  the  caisson  simultaneously  with 
the  sinking  of  the  latter  or  after  it  had  reached  rock,  the  crib 
became  a  necessity.  At  the  present  time  the  tendency  is  toward 
the  elimination  of  the  crib.  As  noted  in  the  preceding  articles 
this  is  done  by  building  a  concrete  shell — virtually  the  pier, 
except  for  the  hole  left  for  the  shafts — before  sinking  op- 
erations are  commenced.  :.. 

If  the  caisson  is  not  to  be  sunk  over  30  feet  the  entire  length 
of  shell  is  cast  previous  to  any  sinking,  beyond  that  of  pitching 
the  caisson,  that  is,  sinking  the  cutting  edge  a  foot  or  two  to 
give  stability;  while  if  the  depth  is  greater  than  (30  feet,  the 
building  and  sinking  are  each  done  in  two  operations.  This 
means  that  the  pier  is  first  built  up  part  way,  sunk  till  the  top 


352 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


reaches  the  surface  of  the  ground,  then  the  remainder  built  and 
the  rest  of  the  sinking  done. 


ART.  119.     SHAFTS  AND  AIR-LOCKS 

Steel  shafts  are  always  used  in  caissons  for  buildings,  and 
owing  to  the  limited  space  a  single  shaft  usually  serves  for  both 
men  and  materials.  For  this  reason,  and  for  the  added  one  that 
it  is  usually  made  removable,  it  differs  somewhat  from  the  shafts 
commonly  used  in  bridge  caissons  (Art.  103).  As  noted  in  Art. 
1 13,  in  the  development  of  pneumatic  caisson  work  for  buildings 
the  tendency  has  been  toward  the  elimination  of  such  parts  as 


FIGS,   uga,  b,  c,  and  d. — Collapsible  and  Removable  Shaft. 

might  weaken  the  finished  pier.  In  eliminating  the  permanent 
steel  shaft  a  considerable  saving  of  money  was  effected  in  that  it 
enabled  using  the  same  shafts  many  times.  The  first  attempts 
were  toward  eliminating  the  steel  shafts  entirely,  not  even  using 
the  same  during  sinking  operations,  the  idea  being  to  employ  a 
shaft  lining  of  molded  concrete,  the  latter  to  be  made  air-tight 
by  painting.  At  present  this  is  done  to  a  considerable  extent 
for  the  lower  lengths. 

One  form  of  collapsible  or  removable  shaft  is  shown  in  Figs, 
iigfl-d,  where  a  shows  a  sectional  elevation  of  the  caisson  with 
the  shaft  lining  in  place;  b  shows  a  plan  of  the  caisson,  while  c 


ART.  119  SHAFTS   AND   AIR-LOCKS  353 

and  d  show  details  of  one  section  of  the  lining.  1  "  Each  section 
was  composed  of  two  approximately  semi-circular  plates 
internally  flanged  for  bolting  to  each  other  along  one  vertical 
edge,  and  a  key  interposed  between  the  opposite  edges  of  the 
plates.  Internal  flanges  at  the  ends  serve  for  bolting  successive 
sections  to  each  other.  Ladder  rungs  were  arranged  conven- 
iently between  the  flanges  of  the  key,  and  vertical  guides  were 
arranged  just  inside  the  line  of  the  end  flanges  to  guide  the 
bucket  past  them." 

The  shafts  should  be  oiled  or  otherwise  protected  from  adher- 
ing to  the  concrete.  The  bottom  section  of  the  shaft  is  usually 
not  made  removable,  but  is  thoroughly  bonded  to  the  concrete 
in  the  crib  (see  Fig.  1146).  This  is  done  to  prevent  the  air  in 
the  working  chamber  from  leaking  between  the  crib  and  the  air 
shaft.  It  also  adds  resistance  against  the  tendency  of  the  air 
to  blow  out  the  shaft  and  air-lock.  A  somewhat  better  form  of 
air-shaft  than  the  one  just  described  has  an  elliptical  section  in 
which  there  is  sufficient  clearance  between  the  bucket  and  the 
ladder  for  a  man  to  pass.  This  eliminates  danger  to  the  men 
in  the  working  chamber  from  the  lodging  of  the  bucket  in  the 
shaft.  Such  a  form  of  shaft  is  shown  in  the  lower  part  of 
Fig.  no/. 

The  air-locks  are  always  placed  on  the  top  of  the  shaft,  and  are 
made  of  steel.  Two  forms,  called  respectively,  the  Moran  and 
the  O'Rourke  air-lock,  have  been  used  almost  exclusively  for 
work  on  building  caissons.  The  feature  most  desired  in  air- 
locks for  materials  is  high  speed  of  operation. 

Figs.  1190  and/2  illustrate  the  Moran  air-lock  for  the  caissons 
of  the  Singer  Building,  New  York.  The  upper  and  lower  doors 
are  not  placed  with  their  vertical  axes  in  the  same  line.  To  begin 
operations  the  upper  door  is  open  and  the  lower  one  closed.  The 
bucket  is  then  let  down  into  the  air-lock,  moved  to  one  side,  the 
upper  door  closed,  the  rope  passing  through  a  hole  in  the  door 

1  Recent  Developments  in  Pneumatic  Foundations  for  Buildings,  by  D.  A. 
USINA,  Trans.  Am.  Soc.  C.  E.,  vol.  61,  page  219,  Dec.,  1908. 

2  From  Foundations  for  the  New  Singer  Building,  by  T.  K.  THOMSON,  Trans. 
Am.  Soc.  C.  E.,  vol.  63,  page  n,  June,  1909. 

23 


354 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


frame,  and  the  valve  in  the  pipe  on  the  left  is  then  placed  in  the 
position  shown  in  the  illustration;  this  permits  the  air  from  the 
shaft  and  working  chamber  below  to  enter  the  air-lock,  and  as 
soon  as  the  pressure  in  the  air-lock  nearly  equals  that  below, 
the  lower  door  opens  and  the  bucket  is  free  to  be  let  down. 
The  lower  door  remains  open  as  long  as  the  bucket  is  below. 


FIGS.  1190  and  /. — Oval  Shaft  Arranged  for  Men  to  Pass  Bucket.     Moran  Air-lock* 

On  coming  out  the  bucket  is  raised  into  the  air-lock,  the  lower 
door  closed,  the  valve  turned  to  connect  the  air-lock  with  the 
outside  air,  which  causes  the  pressure  in  the  latter  to  drop  to 
normal;  this  causes  the  upper  door  to  open  and  the  bucket  is 
taken  out.  Both  doors  are  circular  gasketed  steel  plates 
operated  by  exterior  counterweights.  The  upper  door  is  some- 


ART.  119 


SHAFTS  AND   AIR-LOCKS 


355 


times  provided  with  a  stuffing  box  to  permit  the  passage  of  the 
hoisting  rope  when  the  door  is  closed. 


Elevation.  Sectional  Elevation. 

FIG.   ii.  —  Details  of  Construction  of  O'Rourke  Air-Lock. 


The  O'Rourke  air-lock  is  illustrated  in  Fig.  119  g.     l"  Around 
the  top  opening  is  a  circular  ring,  D,  on  the  inside.     This  open- 
Engineering  News,  vol.  40,  page  364,  Dec.  8,  1898. 


356  PNEUMATIC   CAISSONS   FOR  BUILDINGS  CHAP.  X 

ing  is  closed  by  the  pair  of  oppositely  arranged  convex  swinging 
gates,  E,  the  meeting  edges  of  which  are  packed  so  as  to  make 
an  air-tight  closure.  The  opposite  edges  are  provided  with 
flanges  F,  adapted  to  close  against  the  ring  D,  these  flanges 
having  flap  gaskets,  which  protrude  into  the  air-lock  so  that  the 
air  pressure  striking  them  will  make  an  air-tight  seal  by  pressing 
them  against  the  ring  D.  .  .  . 

"The  gates  E,  are  cut  away  at  the  center  of  the  meeting 
edges,  as  shown  at  H,  to  receive  and  fix  snugly  upon  the  stuffing 
box  J,  banded  with  rubber,  and  having  a  hole  through  the  cen- 
ter for  the  passage  of  the  hoisting  rope.  The  gates  are 
hung  by  the  arms  K,  to  the  common  shafts  G,  one  (M)  being 
fixed  to  the  shaft,  and  the  other  (N)  running  loose.  This 
arrangement  by  means  of  the  bevel  gears  and  idler  m,  n,  and 
o,  allows  the  two  doors  to  be  moved  in  unison  and  in  opposite 
directions  ....  It  will  be  noticed  that  the  levers  have 
counterweights  which  balance  the  doors  and  thus  enable  one 
man  to  operate  the  lock. 

"The  air-lock  has  its  lower  end  closed  by  similar  oppositely 
arranged  swinging  gates,  P,  which  near  their  outer  edges  have 
seats  Q,  which  fit  against  the  ring  R,  with  gaskets  to  secure  a 
tight  fit  ....  Unlike  the  upper  gates  E,  the  lower  gates  -P 
are  swung  by  the  arms  T  from  separate  centers  or  shafts,  U 
and  V.  The  gate  arms  are  rigidly  fixed  to  the  shafts  and  turn 
with  them.  To  secure  opposite  motion  to  the  shafts,  one  is 
operated  by  a  spur  wheel  from  the  other,  as  shown  at  /  and  v, 
the  actuating  force  being  obtained  through  the  lever  O.  The 
admission  and  discharge  of  air  to  and  from  the  locks  is  controlled 
by  the  three-way  cock  X,  operated  by  a  lever  and  bevel  gear 
and  connected  with  suitable  piping  to  the  air-shaft,  there  being 
no  independent  connections  with  the  compressor."  .  .  . 

ART.  120.     SINKING  THE  CAISSON 

Steel  caissons  are  fabricated  at  the  bridge  shops,  assembled 
there  or  at  the  contractors'  yards,  brought  to  the  site  by  teams, 
placed  in  position  by  derricks,  and  sunk.  This  refers  to  the 


ART.  120  SINKING  THE   CAISSON  357 

practice  in  New  York  City.  The  same  general  scheme  is  usually 
employed  with  caissons  of  wood,  the  main  difference  being  that 
the  material  is  fabricated  in  a  wood-working  mill.  The  reason 
for  the  assembly  work  being  done  away  from  the  site  is  the  lim- 
ited space  usually  available  at  the  site,  and  to  the  lack  of 
vacant  lots  in  the  near  vicinity.  Some  idea  of  the  conditions 
obtaining  at  the  site  in  most  of  the  New  York  City  foundation 
work  may  be  obtained  from  Fig.  115^.  As  the  average  caisson 
with  one  section  of  crib  seldom  weighs  over  10  tons  it  is  not  a 
difficult  matter  to  team  them. 

Before  sinking  the  interior  caissons  the  site  is  usually  exca- 
vated down  to  ground-water  level;  at  least  this  is  true  when  the 
cellar  floor  is  to  be  at  or  below  that  elevation.  The  caisson  is 
then  placed  and  one  or  more  sections  of  the  crib  erected  on  the 
same,  or  a  section  of  concrete  shell  cast  if  no  crib  is  to  be  used. 
The  first  few  feet  of  sinking  is  accomplished  without  the  use  of 
air  pressure.  The  material  is  usually  dug  by  hand  and  removed 
with  buckets  although  the  blow-out  process  is  occasionally 
employed.  The  disadvantage  of  the  latter  process  is  due  to  the 
small  volume  of  the  working  chamber  making  it  difficult  to 
maintain  a  constant  pressure  in  the  caisson. 

One  of  the  gravest  problems  connected  with  sinking  caissons 
for  buildings  is  that  of  safeguarding  adjacent  buildings  from 
undermining.  When  a  caisson  is  sunk  through  quicksand 
within  a  few  inches  of  a  building,  which  perhaps  is  founded  on  a 
steel  grillage,  it  is  evident  that  great  care  must  be  taken  not  to 
disturb  this  quicksand  under  the  grillage.  This  fact  usually 
precludes  the  possibility  of  doing  much  'blowing';  that,  is, 
suddenly  reducing  the  air  pressure  in  the  working  chamber  to 
let  the  caisson  sink  a  few  feet,  or  of  using  the  water- jet  on  the 
outside  to  reduce  friction. 

On  account  of  the  large  friction  developed  in  sinking  building 
caissons — much  greater  than  with  bridge  caissons,  where  much 
of  the  crib  is  in  water,  and  therefore  not  subjected  to  friction— 
in  addition  to  excavating  the  material  from  the  caisson  and 
filling  the  crib  with  concrete,  special  devices  must  be  used  to 
promote  sinking.  Greasing  the  sides  of  the  caisson  and  crib 


358  PNEUMATIC   CAISSONS  FOR  BUILDINGS  CHAP.  X 

reduces  the  friction  somewhat  and  it  is  usually  advisable  to  do 
this.  In  some  cases  the  caisson  may  be  pulled  down  by  attach- 
ing lines  to  caissons  already  sunk,  or  to  driven  piles,  as  well  as  to 
timbers  across  the  top  of  the  caisson  to  be  pulled  down.  By  far 
the  most  effective  and  customary  way  is  to  weight  the  caisson 
temporarily  with  pig  iron.  At  present  either  heavy  blocks, 
weighing  as  much  as  4000  pounds  each,  or  ballast  boxes  filled 
with  pig  iron,  are  employed.  A  good  example  of  the  use  of  large 
blocks  may  be  seen  in  Fig.  i  i$c.  Some  of  the  ballast  boxes  hold 
as  much  as  12  ooo  pounds  of  pig  iron.  The  advantage  of  the 
blocks  or  boxes  lies  in  the  fact  that  they  require  no  special  plat- 
form or  yokes  on  the  crib,  and  are  very  quickly  and  easily 
placed  and  removed  by  the  use  of  hoisting  engines. 

Some  of  the  largest  caissons  sunk  to  considerable  depths  have 
each  required  as  much  as  1000  tons  of  this  weighting  material, 
although  the  average  caisson  requires  about  350  tons.  From 
this  it  may  be  seen  that  for  satisfactory  cost  a  means  of  econom- 
ically handling  this  weighting  iron  had  to  be  developed. 

In  many  of  the  earlier  caissons,  such  as  those  of  the  Atlantic 
Mutual  Building,  described  in  Art.  116,  an  excessively  large 
amount  of  temporary  weighting  was  necessary,  on  account  of  the 
concrete  not  being  placed  until  the  caisson  had  reached  its  final 
position.  This  scheme  was  adopted  in  order  that  the  roof  of  the 
caisson  might  be  removed  after  sinking  operations  were  over  and 
the  whole  pier  made  a  single  monolith  of  concrete.  But  later 
caissons  have  preserved  the  latter  feature  without  the  expense  of 
so  much  temporary  weighting.  As  explained  in  Art.  114  this 
was  brought  about  by  using  a  thin  temporary  roof,  only  strong 
enough  to  hold  a  foot  or  two  of  concrete  on  top. 

At  about  the  same  time  that  concrete  roofs  came  into  use  cribs 
were  largely  dispensed  with.  In  their  place  forms  were  used, 
and  as  these  forms  were  of  light  construction,  the  concrete  was 
usually  deposited  in  layers  a  few  feet  high,  and  allowed  to  harden 
before  more  was  added.  As  soon  as  the  concrete  was  sufficiently 
strong  the  forms  were  moved  up  and  another  layer  of  concrete 
placed.  Where  there  are  a  considerable  number  of  caissons  to 
be  sunk,  it  has  become  standard  practice  to  build  the  concrete 


ART.  121  RATE   OF   SINKING  .  359 

as  high  as  possible  before  starting  to  sink.  The  reasons  for  this 
are  as  follows:  First,  sinking  can  be  done  at  a  much  more  rapid 
rate  than  can  the  building  of  the  concrete;  second,  it  saves  on 
the  number  of  times  that  pig  iron  must  be  loaded  and  unloaded; 
and  third,  it  makes  less  temporary  weighting  necessary. 

In  the  caissons  for  the  City  Investing  Building  the  concreting 
was  entirely  finished  before  excavating  in  the  working  chamber 
was  commenced,  although  in  some  cases  caissons  were  sunk  a  few 
feet  to  give  lateral  stability  to  the  tall  shafts  and  to  relieve  the 
excessive  weight  on  the  walls  of  the  working  chamber.  In  the 
Singer  Building,  where  bedrock  was  70  feet  below  the  surface, 
the  concrete  was  built  on  the  caissons  to  one-half  the  estimated 
total  height  before  sinking  was  started,  after  which  the  cais- 
sons were  sunk  until  the  top  of  the  concrete  was  down  to  the 
surface  of  the  ground,  after  which  sinking  operations  were 
stopped,  the  remainder  of  the  concrete  built  and  sinking  re- 
sumed. In  some  of  the  piers  of  the  Municipal  Building 
three  build-ups  were  necessary,  the  maximum  height  of  any' 
one  build  being  60  feet. 

With  these  high  piers  great  care  is  necessary  in  guiding  them 
while  sinking.  For  the  caissons  of  the  United  States  Express 
Building  heavy  horizontal  frames,  braced  with  inclined  struts, 
enclosed  them.  These  frames  took  bearing  on  greased  vertical 
guide  strips  attached  to  the  faces  of  the  concrete  after  the  forms 
were  removed. 

ART.  121.     RATE  OF  SINKING 

Although  showing  large  variations  the  average  rate  of  sinking 
caissons  in  New  York  City  is  high.  This  is  largely  on  account 
of  the  fact  that  rush  jobs  are  customary  there,  and  on  account  of 
the  high  value  of  real  estate,  owners  are  willing  to  pay  well  for 
keeping  the  time  required  for  placing  the  foundations  down  to  a 
minimum.  For  this  reason  many  of  the  records  in  sinking  were 
not  made  under  natural  conditions,  the  cost  being  considerably 
higher  than  if  more  time  had  been  taken. 

The  caissons  of  the  Manhattan  Life  Building,  which  were  both 


360  .     PNEUMATIC   CAISSONS   FOR  BUILDINGS  CHAP.  X 

circular  and  rectangular  in  plan,  the  former  shape  averaging 
about  12  feet  in  diameter  and  the  rectangular  shape  about 
320  square  feet  in  ground  plan,  were  sunk  a  distance  of  34 
feet,  mostly  through  fine  sand.  This  sinking  was  done,  the 
cribs  filled  with  masonry  and  the  working  chamber  and  shafts 
filled  with  concrete,  on  an  average  of  one  caisson  in  eight  days. 
This  corresponds  to  a  sinking  rate  of  4!  feet  per  day. 

The  caissons  for  the  Atlantic  Mutual  Building  (Art.  116)  did 
not  have  their  cribs  filled  with  concrete  until  sinking  was  com- 
pleted. The  material  penetrated  was  largely  quicksand.  One 
caisson  was  sunk  24  feet  in  seven  hours.  Forty-two  caissons 
were  sunk  and  concreted  in  36  days. 

In  the  caissons  of  the  Trinity  Building,  the  average  rate  of 
sinking  through  soft  material  such  as  quicksand  was  about  i 
foot  an  hour,  while  through  hard-pan  it  was  only  about  one- third 
as  much.  These  caissons  were  very  similar  to  those  of  the 
U.  S.  Express  Building  (Art.  114),  and  were  built  up  previously 
to  sinking.  The  rate  as 'here  given  refers  only  to  the  actual 
sinking  and  not  to  the  time  spent  in  building  up  the  caisson 
filling  the  working  chamber,  etc. 

What  is  probably  the  best  record  ever  made  in  caisson  sinking 
was  the  placing  of  87  caissons,  all  over  75  feet  in  depth,  in  60 
days.  These  were  placed  for  the  foundations  of  the  Trinity 
Annex  and  U.  S.  Realty  Buildings  by  the  Foundation  Co.  of 
New  York  City. 

ART.  122.      FILLING  THE  AIR  CHAMBER 

Where  the  caisson  is  to  rest  on  rock  the  surface  should  be 
thoroughly  cleaned  of  loose  and  friable  material  before  placing 
the  concrete  filling.  If  hard-pan,  without  any  pockets  of  loose 
material  in  it,  overlies  the  bedrock  it  is  rarely  advisable  to 
carry  the  cutting  edge  of  the  caisson  more  than  a  few  feet  into 
the  hard-pan.  The  best  method  is  to  stop  sinking  the  caisson 
at  hard-pan  level  and  to  carry  the  excavation  below  the  cutting 
edge  through  the  hard  material  down  to  rock.  In  this  case, 
when  the  concrete  is  placed  it  will  bond  to  the  hard-pan  and  so 


ART.  123  WATER-TIGHT  DAM  OF  WALL  PIERS  361 

reduce  the  load  on  the  base,  whereas  if  the  caisson  is  sunk 
through  the  hard-pan  to  solid  rock  this  bonding  effect  is  lost. 
Another  advantage  of  stopping  the  caisson  at  hard-pan  lies  in 
the  ease  with  which  the  bottom  section  may  be  belled  out  to 
distribute  the  load  over  an  area  larger  than  the  horizontal 
section  of  the  caisson. 

For  caissons  in  which  the  roofs  are  to  be  removed  on  the  com- 
pletion of  the  sinking,  the  working  chamber  is  filled  with 
concrete,  which  is  allowed  to  harden  for  about  two  days,  after 
which  the  roof  and  shafts  are  removed,  and  the  remaining  space 
filled  with  concrete. 

ART.  123.     WATER-TIGHT  DAM  OF  WALL  PIERS 

Many  of  the  large  buildings  of  New  York  City,  built  on  piers 
founded  by  the  pneumatic  process,  have  their  cellar  floors  a 
considerable  distance  below  curb  and  ground- water  levels  which 
necessitates  heavy  dam  construction  around  the  sides.  As 
explained  in  Art.  113  this  dam  construction  is  obtained  by  mak- 
ing the  wall  caissons  rectangular  in  plan  and  sinking  them  with 
a  small  clearance  between  the  ends  of  adjacent  piers,  and  after- 
ward filling  the  space  between  the  piers  with  concrete  or  clay 
to  form  a  continuous  and  water-tight  dam.  Some  clearance 
must  be  left  in  order  to  allow  for  slight  deviations  in  sinking, 
the  usual  amount  allowed  being  from  4  to  18  inches.  The  space 
between  the  piers  may  be  made  water-tight  down  to  bedrock, 
in  which  case  the  use  of  the  pneumatic-caisson  process  may 
sometimes  be  avoided  for  the  interior  column  piers,  or  the  space 
may  be  made  water-tight  to  a  level  a  little  below  the  level  of  the 
cellar  floor. 

The  first  building  using  this  form  of  dam  construction  was 
the  Commercial  Cable  Building.  The  clearance  between  the 
caissons  varied  from  4  to  10  inches.  As  soon  as  the  cais- 
sons were  sunk  3 -inch  pipes  were  jetted  down  in  the  space  be- 
tween the  end  walls,  and  clay  pellets  were  forced  through 
these  pipes  into  the  sand  by  means  of  a  plunger  operated  by  a 
pile-driver.  As  clay  filled  the  space  the  pipes  were  gradually 


362 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


raised  until  the  surface  was  reached,  thus  forming  a  water- 
tight dam  of  clay.  As  soon  as  this  was  completed,  a  section  of 
the  metal  shell  in  the  middle  of  the  ends  was  removed  and  the 
open  space  filled  with  concrete. 

The  caissons  for  the  wall  piers  of  the  New  York  Stock  Ex- 
change Building  were  sunk  with  a  clearance  of  less  than  2  inches, 
the  average  being  i  inch.  That  this  is  too  small  a  clearance 


INSIDE  ELEVATION 

CAISSON  CONNECTIONS, 

BANK  OF  STATE  OF  NEW  YORK 

FlG.    1230. 


CAISSON  CONNECTION, 
STOCK  EXCHANGE. 

FIGS.  1236  and  c. 


was  demonstrated  in  this  work.  Water- tightness  was  obtained 
in  the  following  manner:  As  the  crib  and  working  chamber 
were  filled  with  concrete  semi-circular  wells  were  left  in  the 
ends.  On  the  completion  of  sinking  the  adjoining  wooden 
walls  were  drawn  together  and  bolted  as  shown  in  Fig.  i2T 
The  central  part  of  the  walls  was  then  removed,  thus  combining 
the  two  wells  into  one,  which  was  filled  with  concrete  to  bond 
the  two  piers  together. 
The  spaces  between  the  caissons  of  the  Bank  of  the  State  oi 

1From  Recent    Developments    in    Pneumatic    Foundations  for  Buildings, 
by  D.  A.  USINA,  Trans.  Am.  Soc.  C.  E.,  vol.  61,  Dec.,  1908. 


ART.  123  WATER-TIGHT  DAM   OF   WALL  PIERS  363 

New  York  Building  were  sealed  by  using  two  2-inch  vertical 
strips  of  timber  on  alternate  caissons.  These  str  *ps  were  re- 
cessed into  the  wall  as  shown  in  Fig.  i2T>a.1  On  completion  of 
sinking  the  strips  were  forced  out  against  the  adjacent  caisson 
by  the  simple  arrangement  shown  in  the  illustration. 

The  method  used  for  connecting  the  caissons  for  No.  42 
Broadway  is  illustrated  in  Fig.  I23&.1  On  completing  the  sink- 
ing the  sand  between  the  guide  timbers  was  removed  by  jetting 
the  same  and  the  space  was  then  filled  with  grout. 

The  method  used  in  the  piers  of  the  Trust  Company  of  Amer- 
ica Building,  where  a  1  2-inch  clearance  was  used,  is  illustrated  in 
Fig.  123d.1  As  shown  in  section  XX,  semi-octagonal  spaces  in 
the  center  of  the  ends  of  the  piers  were  left  as  wells  when  the 
concrete  shells  above  the  caissons  were  built,  this  building  being 
done  previously  to  the  sinking.  After  sinking  the  caissons  the 
earth  in  the  1  2-inch  space  between  the  cores  was  excavated  to 
a  depth  of  i  foot  and  the  upper  boards  A  A  were  removed,  cut 
and  placed  in  the  position  A'.  This  alternate  excavating  and 
sheeting  was  carried  down  a  few  feet,  after  which  the  core  planks 
were  removed  and  a  short  section  of  a  steel  air-shaft  cylinder  set 
into  it  and  concreted,  after  which  the  air-lock  was  placed  on  top. 
The  slots  S  were  filled  with  the  shaft  concrete  and  acted  as  keys 
to  prevent  the  blowing  out  of  the  shafts.  Air  pressure  was  then 
put  on  and  the  remainder  of  the  material  excavated  and  boards 
placed  down  to  the  top  of  the  caisson,  after  which  the  whole 
chamber  was  filled  with  concrete. 

A  very  neat  arrangement  was  used  in  the  caissons  for  the 
U.  S.  Express  Building,  where  there  were  clearances  of  from  6  to 
12  inches.  2"  Vertical  grooves  about  2  feet  wide  and  8  inches 
deep  were  made  in  ths  ends  of  the  wall  piers  and  formed,  with 
the  clearances  already  noted  for  the  caissons,  wells,  from  22 
to  28  inches  wide  above  the  tops  of  the  working  chambers. 
Compound  sheet  piles  were  made  with  3-inch  planks  wide 
enough  to  overlap  the  corners  of  adjacent  piers  at  each  joint 


Recent  Developments  in  Pneumatic  Foundations  for  Buildings,  by 
.  A.  USINA,  Trans.  Am.  Soc.  C.  E.,  vol.  61,  Dec.,  1908. 
2  Engineering  Record,  vol.  53,  page  316,  March  3,  1906. 


PNEUMATIC   CAISSONS   FOR  BUILDINGS 


CHAP.  X 


and  were  driven  close  to  the  inner  and  outer  faces  of  the  piers 
so  as  to  cover  the  joints  between  them .... 

"  After  the  sheet  piles  were  driven,  4-inch  pipes  were  jetted 
down  in  the  corners  between  their  edges  and  the  outer  faces  of 


JOINING  CAISSONS  IN 

TRUST  COMPANY  OF  AMERICA 

BUILDING. 

FIG.   i2^d. — Method  of  Sinking  Joint  Well  between  Caissons. 

the  piers,  and  as  they  were  withdrawn  grout  was  forced  through 
them  which  effectually  sealed  the  spaces  between  the  piles  and 
the  piers.  Men  were  then  able  to  enter  the  well  between  the 


ART.  123 


WATER-TIGHT   DAM   OF   WALL  PIERS 


365 


Street  Surface.  rn ^ — _. 


Tern* 


ICot. 


Col.  Foundcrf~ion 
Caisson 


ends  of  the  piers  and  excavate  the  quicksand  and  hard-pan  down 
to  the  tops  of  the  caisson,  caulking  as  they  went  any  slight  leaks 
between  the  sheet  piles  and  the  piers.  Jet  pipes  from  2  to  6 
inches  in  diameter  were  sunk  in  the  narrow  space  between  the 
caissons  and  removed 
or  loosened  the  ma- 
terial down  to  the  cut- 
ting edges.  Grout 
was  then  introduced 
through  them  and 
with  the  sand  and 
broken  stone  already 
there  formed  concrete 
thoroughly  sealing 
the  space  between 
the  working  cham- 
bers. Afterward  the 
well  above  the  work- 
ing chamber  was 
rammed  full  of  ordi- 
nary concrete,  thus 
making  a  solid  key 
which  united  the  wall  v^ 

piers  and    prevented  v| 

leakage."  ! 

Fig.   1230  shows  a- 
line  of   wall   column 
piers  and  the  form  of 
bracing  usually   em- 
ployed.    The    whole 

area  of  the  building  is  first  excavated  to  ground-water  level 
and  sheeted,  after  which  the  wall  piers  are  sunk  and  keyed. 
The  interior  is  then  excavated  to  cellar  floor  level,  the  wall  piers 
being  temporarily  braced  as  the  excavation  proceeds.  The 
final  bracing  of  these  piers  is  done  by  means  of  the  floor  beams 
of  the  building. 


w^m^^ 

'/\*&////'///'//////// 

m^/////v/. 

Wall  Caisson 
-Concrete  Hey 

r 



a 

. 

c 

fj  ~ 

ENG.NEWS., 

FIG. 


1230. — Connection  and  Bracing  of  Wall 
Caissons. 


CHAPTER  XI 
PIER  FOUNDATIONS  IN  OPEN  WELLS 

ART.  124.    OPEN  WELLS  WITH  SHEET-PILING 

A  method  much  used  for  building  foundations  and  occasion- 
ally for  bridge  substructures  is  that  employing  the  open  well. 
This  method  gives  a  type  of  foundation  similar  to  the  caisson 
but  it  is  a  simpler  and  more  economical  process  under  many 
conditions.  Wells  are  sunk  either  by  driving  sheet-piling  and 
then  excavating,  or  by  excavating  first  and  sheeting  afterward. 
The  first  method  is  used  for  quicksand  or  other  material  that 
will  not  stand  up,  while  the  second  method  is  employed  in  clay, 
and  forms  the  type  known  as  the  Chicago  method  because  of  its 
extensive  use  in  that  city.  In  either  case  as  soon  as  the  well  is 
excavated  to  rock  or  hard-pan  it  is  filled  with  concrete  to  form 
the  pier.  The  application  of  the  open-well  method  is  limited  to 
those  cases  in  which  a  moderate  amount  of  disturbance  to  the 
surrounding  material  will  not  damage  adjacent  foundations. 
The  sheet-piling  method  has  been  used  to  depths  of  at  least  60 
feet  and  the  Chicago  method  has  been  used  for  depths  up  to  120 
feet  or  more. 

The  open-well  process  with  sheet-piling,  which  is  used  with 
marked  success  where  rock  may  be  found  at  moderate  depths — 
from  40  to  60  feet — and  where  adjacent  buildings  are  not  in 
danger  of  being  undermined,  is  virtually  the  cofferdam  process 
applied  to  building  foundations.  This  process  differs  from  that 
used  for  bridge  piers  in  that  the  sheet-piling  usually  acts  as  a 
form  for  the  lower  part  of  the  pier  concrete  and  oftentimes  is 
left  in  to  become  more  or  less  a  permanent  part  of  the  pier. 

The  wells  are  either  circular,  square  or  rectangular  in  plan; 
common  sizes  are  about  6  feet  in  diameter  or  on  a  side,  while  for 
rectangular  wells  the  greater  dimension  is  rarely  over  16  feet. 

366 


ART.  124 


OPEN   WELLS   WITH   SHEET-PILING 


367 


Wood,  steel,  or  a  com- 
bination of  both  may 
be  used  for  the  piling. 
If  the  well  is  not  over 
20  to  25  feet  deep  the 
sheet-piling  is  usually 
driven  in  a  single  sec- 
tion, but  for  greater 
depths  two  or  more 
sections  are  used,  the 
upper  sections  being 
large  enough  to  per- 
mit    offsetting    and 
placing  the  lower  sec- 
tions inside. 

The  upper  section 
of    piling    is    driven 
first;     this    may    be 
done  by  hand  or  ma- 
chine.   If  the  driving 
is  not  difficult  this  is 
done  before  excavat- 
ing   is    commenced, 
since  there  is  less  like- 
lihood   for    the    sur- 
rounding material  to 
be  disturbed  through 
flowing  into  the  well 
from  underneath  the 
piling.      Great    care 
should   be   taken   to 
start  the  sheet-piling 
in  its  correct  position 
as  this  will  save  much 
trouble    later.        On 
excavating  the  wells, 
which    is    commonly 


4  Piece  Drum 


2"x6"x/o "  Tongue 
and  GrooveWood 
Lagging 


Plan 


Section 
FIG.   i24a.— Open  Well  for  Railway  Exchange  Building,  St  .Louis. 


368  PIER  FOUNDATIONS   IN   OPEN   WELLS  CHAP.  XJ 

done  by  men  with  picks  and  shovels,  throwing  the  spoil  into 
buckets  lowered  into  the  wells,  bracing  should  immediately  be 
placed. 

As  soon  as  the  first  section  is  driven  and  the  material  exca- 
vated the  second  section  is  started.  On  completion  of  the  work 
to  hard-pan  or  rock,  the  bottom  is  carefully  cleaned  and  leveled 
and  the  lower  section  filled  with  concrete,  a  1-2-4  °r  I~3~5  mix- 
ture being  used,  and  the  sheet-piling  serving  as  a  form.  The 
latter  may  be  withdrawn  after  the  concrete  has  set  or  it  may  be 
left  permanently  in  place.  If  the  sheet-piling  is  to  be  withdrawn 
the  concrete  should  be  protected  in  some  manner  from  bonding 
to  it.  Above  the  lower  section  special  forms  are  usually  made 
for  the  pier  and  the  whole,  including  the  sheet-piling,  with- 
drawn after  the  concrete  has  set. 

Fig.  1240  illustrates  the  cylindrical  well  sunk  to  rock  for  the 
twenty- two  story  Railway  Exchange  Building,  St.  Louis,  Mo. 
The  illustration  indicates  the  character  of  the  material  sunk 
through  as  well  as  the  distance  sunk.  For  the  upper  section, 
8  feet  in  diameter,  2  X  6-inch  tongue-and-grooved  wooden  sheet- 
piling  was  used.  It  was  driven  by  hand  and  braced  by  3X1- 
inch  two-piece  rings.  The  lower  section  had  a  smaller  diameter 
and  was  composed  of  g-inch  Lackawanna  steel  sheet-piling, 
braced  with  four-piece  wooden  drums  made  of  i2Xi4-inch 
material  with  cast-iron  ball-and-socket  joints  at  the  ends.  After 
the  piling  was  driven  the  material,  loosened  and  kept  in  sus- 
pension by  a  i  J-inch  jet  under  100  pounds  pressure,  was  removed 
with  pumps.  On  completion  of  the  excavation  a  3-foot  layer 
of  1-15-2  concrete  was  deposited  to  seal  the  bottom,  no  pump- 
ing being  done  in  the  meantime.  After  allowing  the  concrete 
to  set  for  five  or  six  hours  the  water  was  pumped  out  and  the 
lower  cylinder  filled  with  concrete,  the  braces  being  removed 
at  the  same  time.  The  sheet-piling  was  left  in  place. 

The  square  piers  of  the  Bamberger  Building,  Newark,  N.  J., 
were  built  in  two  sections,  with  timber  sheet-piling  above  and 
steel  sheet-piling  below.  They  present  a  good  example  of 
very  careful  guiding  of  the  piling.  Each  cofferdam  was  12  feet 
square  on  top  and  the  upper  section  was  lined  with  3-inch 


ART.  124 


OPEN   WELLS    WITH   SHEET-PILING 


369 


tongue-and-grooved  planks  20  feet  long.  The  piling  was  assem- 
bled on  horizontal  skids  to  make  panels  12  feet  wide  with  trans- 
verse cleats  on  top  and  bottom. 

A  pit  was  first  excavated  and  in  it  was  placed  the  bracing 
frame  shown  in  the  right-hand  drawing  of  Fig.  1246.  The 
three  sets  of  horizontal  ioX  lo-inch  frames  were  braced  together 
with  diagonal  planks  and  the  two  upper  frames  rested  on  ioX  10- 
inch  posts  4  feet  long.  The  ends  of  the  rangers  were  halved  and 
were  connected  by  short  ioX-inch  planks. 


'4 

/ 

* 

\ 

\ 

-(* 

y 

\ 

i 

<& 

z 

V 

©  1  « 

FIG.   1246. — A  Side  Panel  and  Frame  of  Cofferdam.  ' 

luThe  side  panels  of  vertical  sheeting  planks  are  lifted  by  a 
derrick,  the  tackle  being  attached  to  a  bridle  connected  to  the 
ends  of  a  pair  of  horizontal  planks  tightly  clamped  to  the  upper 
end  of  the  assembled  panel  (see  left-hand  illustration,  Fig. 
1246).  After  the  four  panels  are  set  in  place  against  the 
faces  of  the  rangers  forming  the  interior  framework  they  are 
secured  by  light  yokes  of  horizontal  timbers  and  tension  rods 
screwed  up  tight,  after  which  the  temporary  cleats  are  removed 
and  the  sheeting  is  driven  by  light  steam-hammers  as  the 
excavation  progresses  inside,  the  rangers  being  forced  down  as 
necessary." 

Fig.  1 240  shows  the  sinking  of  cylindrical  wells  for  the  foun- 
dations of  the  Kinney  Building,  Newark,  N.  J.  After  being 
assembled  by  stiff-leg  derricks  the  steel-piling  units  were 
clamped  together  by  outside  wire  cables  holding  them  against 
inside  ranger  frames  spaced  from  2\  to  5  feet  apart  and  made 
from  two  thicknesses  of  3  X  5-inch  scarfed  planks  with  five  to 


1  Engineering  Record,  vol.  64,  page  457,  Oct.  14,  1911. 
24 


370  PIER   FOUNDATIONS   IN   OPEN   WELLS  CHAP.  XI 

seven  pieces  in  each  course.  The  piling  was  driven  to  bottom 
before  any  excavating  was  done  and  was  removed  after  the  well 
was  filled  with,  concrete. 

ART.  125.     OPEN  WELLS  WITH  SHEETING:  THE  CHICAGO 

METHOD 

The  soil  conditions  in  the  downtown  or  business  district  of 
Chicago,  where  most  of  the  heavy  buildings  are  located,  are 
peculiar  and  have  led  to  a  special  type  of  foundation  being  used 
for  many  of  the  heavy  structures.  For  a  distance  of  about 
14  feet  below  the  street  curb  the  soil  consists  of  loam  and  made 
ground;  below  this  there  is  a  layer  of  clay  having  a  thickness 
of  from  70  to  80  feet,  which  overlies  hard-pan  or  coarse  gravel 
and  solid  rock.  The  upper  6  to  1 2  feet  of  this  clay  is  hard  and 
stiff  and  forms  the  bed  on  which  rest  many  steel  grillage  founda- 
tions (Arts.  151,  152,  156)  which,  dating  from  1878,  were  so 
extensively  used  in  that  city.  Below  this,  the  clay  becomes 
softer  and  remains  so  down  to  the  hard-pan,  which  has  a 
thickness  of  from  10  to  20  feet.  In  general  this  softer  clay 
differs  from  that  above  only  in  the  larger  amount  of  water 
contained  in  it.  In  places  pockets  of  quicksand  are  present 
in  the  soft  clay. 

The  clay  is  sufficiently  stiff  to  permit  sinking  wells  by 
excavating  the  clay  in  sections  about  4  feet  deep,  each  section 
being  sheeted  with  2  X  6-inch  or  3  X  6-inch  planks  in  4-foot 
lengths  as  soon  as  the  section  is  excavated.  In  some  cases 
the  sheeting  has  been  made  of  sheet  metal.  The  wells  vary 
from  about  3  to  12  feet  in  diameter.  Thus  this  method  differs 
from  the  sheet-piling  method  essentially  in  that  the  excava- 
tion is  made  before  the  lining  is  placed,  while  in  the  sheet- 
piling  method  the  lining  is  always  placed  in  advance  of  the 
excavation. 

DIGGING  THE  WELL. — The  wells  are  excavated  by  hand  to 
the  required  diameter,  from  one  to  four  men  working  in  a  single 
well.  As  soon  as  a  section  is  excavated  tongue-and-grooved 
lagging,  2  or  3  inches  thick  and  not  over  6  inches  wide  and 
beveled  to  form  a  true  circle,  is  placed.  Two  or  perhaps  three 


sr 


ART.  125  OPEN   WELLS   WITH   SHEETING  371 

iron  hoops,  f  by  3  inches  in  section,  or  angle-iron  hoops,  are 
used  to  brace  the  sheeting  of  eacli  section.  These  hoops  are 
made  in  semi-circular  form  with  their  ends  bent  inward  to  form 
flanges  which  are  bolted  together  as  shown  in  Fig.  1 240.  As 
soon  as  the  bracing  for  one  section  is  placed  the  next  section  is 
excavated  and  the  lagging  for  that  section,  abutting  against  the 
lagging  for  the  section  above,  is  placed,  and  this  cycle  is  repeated 
until  the  hard  material  is  reached. 

Care  must  be  exercised  to  have  the  lagging  fit  tightly  against 
the  clay  in  order  to  prevent  any  flow  of  the  same.  As  this  is 
somewhat  difficult  to  accomplish  with  the  above  described  type 
of  hoops,  another  form  has  been  invented  by  J.  W.  JACKSON. 
Each  brace  consists  of  four  sections  of  steel  tee  bars  bent  to 
form  a  circular  sectional  rib  bearing  against  the  lagging,  and  of 
a  hollow  central  hub  to  which  are  attached  jack  screws  radiating 
from  the  hub  like  the  spokes  of  a  wheel.  The  heads  of  these 
jack  screws  are  fitted  to  shoes  on  the  horizontal  web  of  the 
circular  rib  or  rim.  As  many  jacks  as  necessary  may  be  used  but 
not  less  than  four,  one  for  each  section  of  the  rib.  The  jacks 
may  be  set  up  to  compress  the  surrounding  material  as  much 
as  desired. 

The  spoil  is  removed  from  the  wells  by  buckets  operated  by  a 
windlass  or  other  arrangement.  For  small  jobs  the  windlass 
may  be  worked  by  hand  but  where  a  large  number  of  piers  are 
being  sunk  power  is  used.  The  Thomas  Elevator  Co.  of 
Chicago  build  a  multiple  spool  hoist  which  will  operate  a  num- 
ber of  wells  by  one  motor,  each  one  independently  of  all  others 
(see  Eng.  News,  vol.  65,  page  133,  Feb.  2,  1911). 

The  lagging  and  bracing  are  sometimes  removed  as  the  con- 
crete is  placed,  but  if  the  surrounding  material  is  at  all  soft 
they  are  usually  left  in.  A  1-3-5  mixture  of  concrete  is  com- 
monly used  for  the  filling. 

Where  the  pier  rests  on  hard-pan  the  lower  part  is  ordinarily 
belled  out  to  about  twice  the  diameter  of  the  pier,  the  belling 
being  done  at  an  angle  of  approximately  45  degrees.  The  unit 
bearing  pressure  allowed  is  about  7  tons  per  square  foot  for  hard- 
pan  and  about  30  tons  for  rock. 


37 2  PIER   FOUNDATIONS  IN   OPEN   WELLS  CHAP.  XI 

APPLICATIONS. — The  first  building  in  Chicago  and  the  first 
in  the  United  States,  with  the  exception  of  the  City  Hall  of 
Kansas  City,  to  have  this  type  of  foundation  was  the  Chicago 
Stock  Exchange,  built  in  1892.  This  structure  was  founded  on 
piles  and  on  piers  sunk  by  the  Chicago  method,  the  latter 
being  used  since  it  was  feared  that  the  jarring  of  pile  driving 
would  disturb  the  foundations  of  adjacent  buildings. 

For  the  wells  of  the  City  Hall  foundations  in  Kansas  City  a 
metal  shell  lining  was  used  instead  of  wooden  lagging  and  the 
piers  were  constructed  of  brick- work  instead  of  concrete. 

The  foundations  for  the  new  City  Hall  of  Chicago  were  com- 
posed of  circular  concrete  piers  from  4  to  10  feet  in  diameter  and 
seated  on  bedrock  96  to  120  feet  below  street  grade.  Three- 
inch  tongue-and-grooved  lagging  in  4-foot  lengths  was  used. 
The  clay  spoil  was  dug  by  hand,  one  to  four  men  working  in  a 
well  at  one  time.  The  buckets  held  3  or  4  cubic  feet  and  were 
raised  and  lowered  by  means  of  timber  tripods  set  up  over  the 
wells.  A  drive  wheel  was  placed  on  one  side  of  each  tripod  and 
was  connected  to  a  shaft  that  carried  a  winding  spool.  A  single 
endless  cable  on  a  hoisting  engine  connected  with  a  number  of 
the  driving  wheels — the  tripods  being  set  up  in  straight  rows — 
and  thus  readily  served  seven  or  eight  wells. 

In  applying  the  Chicago  method  modifications  may  be  made 
to  suit  local  conditions;  for  instance,  the  sheet-piling  and  the 
sheeting  method  may  be  combined  in  the  same  well.  This  was 
done  in  the  foundation  work  for  the  Hotel  Brevoort,  Chicago, 
where  the  presence  of  a  high  building  nearby  made  necessary  the 
use  of  steel  sheet-piling  for  a  depth  of  30  feet,  while  below  this  the 
ordinary  lagging  was  used. 

Fig.  125  a  shows  the  details  of  the  65-foot  wells  used  for  the 
foundations  of  a  double- track  bascule  bridge  of  the  Baltimore 
&  Ohio  Railroad  in  South  Chicago.  The  surface  of  the  ground 
was  at  about  water-level  and  for  the  upper  18  feet  the  material 
was  quicksand,  there  being  below  this  an  impervious  stratum  of 
soft  blue  clay  which  extends  to  rock. 

A  cofferdam  made  of  3Xi2-inch  tongue-and-grooved  sheet- 
piling  in  2i-foot  lengths  was  driven  through  the  sand  to  the 


ART.  126  THE   GROUTING  PROCESS  373 

stiff  clay  and  braced  with  three  tiers  of  12  X 1 2-inch  rangers,  with 
45-degree  knee  braces  at  the  corners.  The  bracing  was  placed 
as  the  well  was  excavated.  At  the  bottom  a  1 2-foot  diameter 
well  was  sunk  and  lined  with  lagging  composed  of  courses  of  No. 
20  corrugated  iron  in  2-foot  widths  and  of  lengths  equal  to  the 
circumference  of  the  well.  Vertical  2  X  2-inch  flange  angles 
about  23  inches  long  were  riveted  to  the  rims  of  both  ends  of 
each  section  and  through  open  holes  in  the  outstanding  legs 
were  bolted  together  when  placed  in  position  to  make  complete 
rings. 

After  placing  the  first  section  12  inches  of  concrete  was  depos- 
ited between  the  same  and  the  lower  part  of  the  cofferdam  to 
seal  the  space  between  the  cofferdam  and  well.  As  the  material 
was  excavated  additional  rings  of  lagging  were  placed,  each  one 
overlapping  the  one  above  it  by  a  single  corrugation.  No  bolt- 
ing of  horizontal  joints  was  done  and  no  bracing  was  used. 

A  10-  to  i2-foot  layer  of  quicksand  with  its  surface  100  feet 
below  the  street  curb  was  struck  in  sinking  the  wells  of  the  Chi- 
cago Edison  Go's,  building.  Below  this  there  was  a  layer  of 
boulders  overlying  the  bedrock  and  these  boulders  varied  from 
cobble-stone  size  to  5  feet  in  diameter.  On  reaching  quicksand 
the  usual  method  was  abandoned  and  steel  cylinders  in  three 
sections,  with  vertical  joints  flanged  with  angle-iron  connections, 
were  sunk.  As  the  quicksand  was  removed  from  the  interior 
these  cylinders  sank  by  their  own  weight  until  the  boulders 
were  reached.  These  had  to  be  drilled  and  split  open  to  permit 
the  caissons,  aided  by  jacks,  to  pass  through. 

In  the  wells  for  the  foundations  of  the  Northwestern  Railroad 
Terminal  (see  Eng.  News,  vol.  62,  page  554,  Nov.  18,  1909) 
the  pneumatic  caisson  process  was  used  when  a  heavy  water- 
bearing stratum  just  above  rock  was  struck. 

ART.  126.     THE  GROUTING  PROCESS 

The  general  idea  of  the  grouting  process  is  to  inject  fluid  cement 
between  and  among  materials  already  in  place  and  thus  cement 
the  mass  into  a  solid  concrete.  The  process  may  be  used  for 


374  PIER  FOUNDATIONS  IN   OPEN  WELLS  CHAP.  XI 

forming  new  foundations  or  for  repairing  old  ones.  For  foun- 
dations on  land  two  general  methods  may  be  used:  The  whole 
foundation  bed,  down  to  rock  or  other  firm  material,  may  be 
turned  into  concrete  in  situ  and  the  piers  built  directly  upon  it; 
or  a  ring  of  concrete  may  be  formed  around  the  site,  forming  a 
sort  of  cofferdam,  after  which  the  interior  may  be  excavated 
down  to  solid  material  and  the  substructure  built  within  it. 
The  latter  method  will  give  a  more  reliable  foundation  but  a 
more  expensive  one.  In  using  the  former  method  it  is  a  difficult 
matter  to  prevent  pockets  of  uncemented  material  from  being 
present.  It  seems  that  this  process  may  be  used  satisfactorily 
for  any  material  varying  from  the  size  of  broken  stone  down  to 
fine  sand.  Clayey  material  cannot  be  grouted. 

Two  methods  have  been  developed  for  the  application  of  the 
grouting  process;  the  first  uses  the  cement  in  the  form  of  a  fluid, 
and  the  second  in  its  dry  state.  The  first  may  be  subdivided 
into  two  methods,  one  being  used  where  fine  material  is  encount- 
ered and  the  other  for  coarse  material. 

Where  cement  grout  is  used  in  fine  material  two  pipes,  a 
short  distance  apart,  are  first  driven.  Water  is  then  pumped 
down  one  pipe  and  in  taking  a  course  of  least  resistance  will 
come  up  the  other  pipe,  thus  cutting  out  a  channel  between  the 
two  pipes.  By  using  a  number  of  pipes  as  many  channels  as 
desired  may  be  made.  As  soon  as  a  well-developed*  channel  is 
formed  cement  grout  is  pumped  through  the  pipe  instead  of  the 
water.  When  the  grout  appears  in  the  outlet  pipe  the  latter  is 
closed  by  a  valve  and  the  pumping  continued,  thus  forcing  the 
grout  to  permeate  the  sand  around  the  channel.  In  this  way  a 
stratum  of  solid  mortar  or  concrete  is  formed;  by  employing  the 
same  scheme  at  various  depths  the  whole  mass  becomes 
solidified. 

Where  medium-sized  material  is  encountered  it  is  often  only 
necessary  to  drive  a  row  of  pipes  and  pour  the  grout  into  them, 
the  head  being  sufficient  to  force  the  grout  throughout  the 
material. 

In  coarse  material  the  difficulty  lies  in  keeping  the  grout 
within  bounds  and  preventing  it  from  spreading  out  in  thin 


ART.  126  THE   GROUTING  PROCESS  375 

layers  and  running  into  adjacent  territory,  or  below  the  level 
at  which  it  is  desired  to  form  the  concrete.  This  difficulty  may 
be  overcome  by  using  the  principle  of  successive  accretions. 
In  using  this  method  only  a  small  amount  of  grout  is  poured 
into  any  one  pipe  at  a  time.  After  this  has  had  time  to  set, 
more  grout  is  poured  in  and  the  operation  repeated  until  a 
solid  floor  of  concrete  is  made.  Walls  may  be  made  in 
the  same  manner,  after  which  the  interior  may  be  filled 
with  grout  or  excavated. 

The  method  which  employs  dry  cement  is  as  follows:  The 
cement  is  blown  through  a  if -inch  pipe,  drawn  to  a  point  at  the 
lower  end,  in  which  there  are  three  or  more  holes  of  about  f  inch 
diameter.  The  pipe  is  free  to  be  raised  or  lowered,  and  is  con- 
nected at  its  upper  end  with  an  air-pressure  supply  pipe.  To 
this  air-pressure  pipe,  suitable  connections  are  made  of  suit- 
able branches,  stop  cocks,  etc.,  and  by  means  of  an  injector 
cement  powder  is  fed  into  the  air  current.  The  cement  powder, 
by  means  of  an  air  current  is  forced  through  the  small  openings 
in  the  lower  end  of  the  pipe  and  is  driven  into  the  sand.  In 
consequence  of  the  boiling  action  caused  by  the  air  bubbles 
running  through  the  water  in  the  sand  the  cement  is  thoroughly 
mixed  with  the  latter,  and  as  soon  as  injecting  is  stopped  the 
sand  with  the  particles  of  cement  clinging  to  it  settles  into  place 
and  forms  concrete  or  mortar.  The  volume  of  cement  used 
should  be  about  one-fifth  the  volume  of  the  sand.  In  fine 
material  each  sinking  of  the  pipe  will  cover  about  i  square 
foot  of  ground  and  the  cement  must  be  forced  out  at  different 
elevations,  the  pipe  being  slowly  drawn  up  as  the  cement  is 
blown  into  the  sand.  The  dry  method  is  seldom  used  at 
present.  For  further  details  concerning  this  method  the  reader 
is  referred  to  an  article  by  FR.  NEUKIRCH  in  Transactions  Amer- 
ican Society  of  Civil  Engineers,  vol.  29,  page  639,  Sept.,  1893, 
entitled  Improved  Method  of  Constructing  Foundations  under 
Water  by  Forcing  Cement  into  Loose  Sand  or  Gravel  by  Means 
of  Air  Pressure. 


376  PIER   FOUNDATIONS   IN    OPEN   WELLS  CHAP.  XI 

ART.  127.     APPLICATIONS  AND  TESTS 

The  exclusion  of  water  from  the  site  is  one  of  the  most  expen- 
sive items  connected  with  foundation  work.  The  economy  of 
the  grouting  process  lies  in  the  fact  that  the  necessity  for  doing 
this  may  be  avoided  or  else  it  may  be  done  cheaply. 

Grouting  has  been  used  quite  extensively  for  repairing  dams, 
quay  walls,  etc.,  where  the  water  has  washed  out  the  filling.  In 
such  cases  it  is  customary  to  sink  pipes  and  pour  cement  grout 
into  them,  the  pressure  head  on  the  grout  being  sufficient  to 
force  it  into  place.  It  has  been  found  that  the  pressure  head 
of  a  column  of  grout  is  about  double  that  of  water.  For  an 
example  of  the  use  of  the  grouting  process  for  the  foundation 
of  a  cylinder  caisson  see  Art.  102. 

The  left  abutment  (on  land)  of  a  concrete  arch  bridge  at 
Ehingen,  Germany,  was  founded  on  a  bed  of  concrete  formed 
in  place  by  the  injection  of  grout.  The  material  was  water- 
bearing gravel.  1 "  Twelve-foot  lengths  of  ij-inch  pipe,  with 
an  iron  driving  point  loosely  inserted  in  the  lower  end,  were 
driven  down  to  rock,  and  then,  by  raising  a  few  inches,  lifted 
clear  of  the  driving  point.  Cement  grout  was  then  pumped  in 
until  a  rapid  rise  in  pressure  indicated  saturation;  the  pipe  was 
then  drawn  up  a  small  distance,  grout  pumped  in  again  to 
saturation,  and  so  on."  Pipes  were  driven  at  intervals  of  18 
and  20  inches  and  test  excavations  made  afterward  showed  a 
very  good  quality  of  concrete. 

1  "To  found  the  two  river  piers,  cofferdams  of  sheet-piling 
were  driven  to  rock  and  made  water-tight  by  injection  of  cement 
through  pipes  driven  around  them.  In  the  case  of  one  of  the 
piers,  pipes  were  driven  inside  as  well  as  outside,  with  the  result 
that  nearly  the  whole  mass  in  the  interior  of  the  cofferdam  was 
cemented  into  a  block  of  concrete.  On  account  of  some  layers 
of  sand,  however,  about  one-half  of  this  mass  was  broken  out 
again  and  the  pier  regularly  built  up  of  concrete  above  the  re- 
maining conglomerate.  At  the  other  pier,  the  cementing  was 
carried  out  only  around  the  outside  of  the  cofferdam,  making 

1  Engineering  News,  vol.  47,  page  35,  Jan.  9,  1902. 


ART.  127  APPLICATIONS   AND   TESTS  377 

is  perfectly  tight.  The  interior  was  then  excavated  and  the 
concrete  of  the  pier  built  up  directly  on  the  rock." 

A  good  example  of  the  successive  accretion  method  of  grout- 
ing is  that  of  rebuilding  one  of  the  piers  of  a  bridge  on  the  New 
York  Northern  Railroad,  across  Croton  Lake,  N.  Y.  The  pier 
was  about  22  by  32  feet  in  plan  and  about  7  feet  high.  It 
resed  on  a  crib  35  by  47  feet  in  plan,  made  of  4-inch  planks  laid 
cob  fashion,  and  divided  into  nine  compartments,  filled  with 
stone.  The  top  of  the  crib  was  about  5  feet  below  water.  The 
problem  was  to  make  a  solid  pier  out  of  the  one  which,  as 
originally  built,  was  not  filled  with  masonry  but  with  rocks, 
sticks,  dirt  and  all  sorts  of  rubbish,  there  being  merely  a  shell 
of  masonry  around  the  outside.  As  stated  by  the  engineer, 
R.  L.  HARRIS:  lt(  We  wanted  a  tight  bottom  at  any  level  below 
the  top  of  the  crib  and  tight  sides  thence  to  the  water  surface. 
The  idea  was  to  use  the  materials  that  were  in  place,  and  make  a 
caisson  therein  without  disturbance,  by  cementing,  for  the 
floor  of  the  caisson,  a  portion  of  the  loose  mass  of  irregular 
stone  filling  in  the  crib  at  any  level  below  the  top  of  the  crib; 
and  for  walls,  to  cement  from  thence  to  the  water  surface,  or  as 
high  as  necessary  to  make  a  good  connection  with  the  shell; 
this  could  then  be  pumped  out,  the  interior  carefully  excavated 
to  the  crib,  and  the  space  filled  with  concrete  rammed  in  layers 
to  the  top  of  the  old  shell." 

Some  of  the  interior  masonry  was  removed  from  the  top  and 
then  holes  were  worked  among  the  stones  extending  a  few  feet 
below  the  top  of  the  crib.  "  A  long  nozzle  of  if -inch  iron  pipe, 
connected  to  the  discharge  pipe  of  a  No.  2  Douglas  hand  force 
pump,  was  inserted  in  one  of  these  holes  to  its  bottom,  water  was 
rapidly  pumped  through  for  a  few  minutes,  then  the  suction 
hose  was  suddenly  transferred  to  a  reservoir  of  grout,  composed 
of  portland  cement  and  fine  sharp  sand,  in  equal  parts,  mixed 
immediately  before  use ;  a  small  quantity  only  of  the  grout  was 
slowly  forced  through,  and  the  nozzle  was  then  withdrawn  but 
the  hole  maintained,  and  the  same  operation  was  continued  at 

*A  cofferdam  without  Timber  or  Iron,  by  R.  L.  Harris,  Trans.  Am.  Soc. 
C.  E.,  vol.  24,  page  234,  March,  1891. 


378  PIER   FOUNDATIONS   IN   OPEN   WELLS  CHAP.  XI 

other  holes,  seldom  returning  to  any  hole  the  same  day;  the 
belief  being,  that  in  quiet  water  the  cement  would  accrete  on  the 
surface  of  irregular  stones  at  and  below  the  level  of  the  injection, 
and  that  by  consecutive  slight  accretions  at  proper  intervals 
of  time  the  voids  between  them  would  be  filled."  The  results 
were  successful. 

TESTING  THE  GROUTING  PROCESS. — Although  many  exam- 
ples exist  of  the  successful  application  of  this  method,  yet  there 
is  always  some  uncertainty  regarding  the  degree  of  success  in  any 
particular  case.  To  test  its  reliability  the  Louisville  &  Nashville 
Railroad  had  some  interesting  experiments  made,  a  complete 
description  of  which  may  be  found  in  Engineering  News,  vol. 
69,  page  979,  May  8,  1913. 

The  most  interesting  experiment  made  was  in  gravel,  where 
bedrock  was  23  feet  below  the  surface  and  the  water-level  8  feet 

24*  Outside  dfam. 
:  2'  Inside  diatn. 


**?*           7  Rows  of  18  Holes 

ir-5  r^f 

~^*£fij 

3  m 

^^e°T 

>l          i 

-^  r*         ? 

r<  - 
\<-- 

-  -.—  I.I  - 
-2.0-- 

,,       i    PerforaTions 
<—  6  ->H      in  Point 

FIG.   i27a. — Well  Point  on  End  of  Grouting  Pipe. 

below.  An  analysis  of  the  gravel  gave  the  following  percentage 
in  its  mechanical  composition:  Coarse  gravel,  12,  very  fine 
gravel,  34,  sand,  44,  and  silt,  10.  Two-inch  pipe  in  5-foot  sec- 
tions and  with  a  well  point,  illustrated  in  Fig.  1270,  were  driven 
to  rock  on  the  circumference  of  a  circle  15  feet  in  diameter  and 
with  a  spacing  of  about  3  feet.  An  average  unit  pressure  of  20 
pounds  was  sufficient  to  force  the  grout  into  the  gravel,  although 
at  times  60  pounds  would  not  clear  the  pipe.  The  pipe  was  slowly 
withdrawn  as  the  grout  was  forced  in,  the  one  operation  follow- 
ing the  other,  enough  grout  being  forced  in  to  fill  all  voids  for  a 
distance  of  2  feet  out  from  the  center  of  the  pipe.  On  allowing 
the  material  to  harden  and  then  excavating  the  core,  it  was  found 
that  the  wall  was  sufficiently  good  to  allow  the  water  to  be 
pumped  down  within  2  feet  of  the  rock. 


ART.  128 


THE   FREEZING   PROCESS 


379 


Fig.  1276  shows  the  appearance  of  the  concrete  after  removing 
the  core.  The  grout  followed  the  path  of  least  resistance  which 
was  essentially  upward.  In  coming  up  much  of  the  silt  in  the 
gravel  floated  on  the  grout.  In  addition  to  the  latter  effect 
the  grouting  below  tended  to  disturb  the  material  at  the  top, 
causing  the  fine  material  there  to  separate  from  the  coarse,  thus 
leaving  a  very  porous  layer  just  above  water-level,  with  a  layer 


I5'(Diam.of  Circle)  — 
Too  of  Concrete 


FIG.   1276, — Typical  Cross-section  of   Concrete  Cylinder  Formed  by  the  Circle  of 

Grouting  Pipes. 

of  silt  at  water-level.  As  a  consequence,  for  4  feet  above  the 
water  surface  the  best  concrete  formed  and  this  extended  across 
the  cylinder  and  had  to  be  dug  out  with  picks  on  excavating 
the  core.  On  the  other  hand  at  the  mud  seam  no  concrete 
formed  even  at  the  pipe.  Below  the  water-level  the  concrete 
was  irregular  and  not  especially  good. 

ART.  128.    THE  FREEZING  PROCESS 

The  idea  of  freezing  the  soil,  as  an  aid  to  excavation,  has  ex- 
isted for  many  years,  and  although  it  has  attained  a  considerable 
degree  of  success  in  the  sinking  of  mine  shafts,  particularly  in 


380  PIER   FOUNDATIONS  IN   OPEN   WELLS  CHAP.  XI 

Germany  and  other  foreign  countries,  it  has  seldom  been  applied 
to  foundations.  However,  owing  to  the  inherent  possibilities 
of  this  process  for  foundations  at  great  depths  the  principles 
are  worthy  of  careful  study. 

The  presence  of  water  causes  the  principal  difficulties  in 
foundation  work,  especially  when  water  is  present  in  very  fine 
sand,  forming  what  is  known  as  quicksand.  If  the  water  can  be 
frozen  the  work  becomes  easy.  In  the  method  invented  in  1884 
by  F.  H.  POETSCH  M.  D.,  a  Prussian,  tubes  are  driven  around  the 
outside  of,  or  into  the  soil,  all  over  the  site  to  be  excavated,  and 
a  freezing  mixture  is  made  to  circulate  through  these  pipes, 
which  gradually  transforms  the  soil  into  a  non- water-carrying 
solid  mass,  after  which  the  excavation  can  easily  be  made.  If 
the  pipes  are  driven  to  a  non-water-bearing  stratum  it  is  only 
necessary  to  freeze  a  wall  around  the  site  but  if  an  impervious 
stratum  is  not  reached  the  whole  site,  or  a  ring  around  the  site 
and  a  layer  of  soil  near  the  bottom  must  be  frozen. 

Long  water-tight  tubes  closed  at  the  bottom,  from  4  to  6 
inches  in  diameter  and  spaced  about  3  feet  apart,  are  first 
driven  through  the  mass  to  be  frozen.  Inside  of  these  tubes  are 
placed  small  pipes,  from  i  to  ij  inches  in  diameter,  which  are 
open  at  the  bottom  or  have  openings  in  their  sides  near  the  bot- 
tom. A  considerable  number  of  the  small  circulating  tubes  are 
joined  together  by  a  larger  pipe,  and  the  larger  or  freezing  tubes 
are  capped  and  joined  together  by  another  pipe.  A  circuit  is 
then  formed  and  cold  brine  is  drawn  from  a  tank,  pumped  down 
the  circulating  tubes,  up  through  the  freezing  tubes,  and  back  to 
the  freezing  machine.  For  shaft  sinking  the  pipes  are  usually 
placed  around  the  circumference  of  a  ring  with  perhaps  a  few 
inside  which  are  so  insulated  that  they  freeze  only  the  bottom 
of  the  shaft. 

What  is  said  to  be  the  first  application  of  this  process  to 
building  foundations  is  that  for  the  substructure  of  a  depart- 
ment store  in  Berlin.  Fig.  1280  illustrates  the  conditions 
obtaining  at  the  site  as  well  as  the  general  plan  of  the  process. 
The  subsoil  was  a  quicksand  with  ground  water-level  about  13 
feet  below  the  curb.  The  foundations  of  adjoining  buildings 


ART.  128 


THE    FREEZING    PROCESS 


381 


were  10  feet  below  the  curb,  while  the  excavation  for  the  new 
structure  had  to  be  carried  to  a  depth  of  36  feet  below  the  curb. 
Sheet-piling  was  first  used  but  as  soon  as  the  excavation 
reached  below  water-level  the  sand  from  under  the  adjoining 
buildings  on  one  side  of  the  lot  commenced  boiling  up  in  the 


A 

^  ooooooooooooo 

I 

'-The  freezing  pipes  were 
placed  about  6  sit  from 

ihe  sides  of  the  adjoining 
building 

.--56'--. 

Y 

FIG.   i28a. — Building  Foundation  Constructed  under  the  Freezing  Process. 

excavation,  causing  several  structures  to  settle  and  crack. 
The  freezing  process  was  then  adopted.  Freezing  pipes  5  inches 
in  diameter  and  about  yV  inch  thick  were  sunk  on  3 -foot  cen- 
ters as  shown  in  the  illustration  and  extended  59  feet  below  curb 
level.  The  circulating  pipes  were  i  inch  in  diameter  and  were 
connected  to  a  supply  header  at  the  top,  while  the  5-inch  pipes 


382  PIER  FOUNDATIONS  IN   OPEN  WELLS  CHAP.  XI 

were  connected  to  a  drain  header.  The  liquor  passed  through 
the  circulating  pipes  with  a  velocity  of  n^  feet  per  minute. 
About  four  weeks  after  the  brine  was  started  the  ground  was 
frozen  a  sufficient  distance  to  begin  excavating,  after  the  com- 
pletion of  which,  the  foundation  was  placed.  The  cost  is 
said  to  have  been  lower  than  if  the  pneumatic  caisson  process 
had  been  employed. 

Only  under  special  circumstances,  or  where  no  other  process 
can  be  adopted,  or  where  a  refrigerating  plant  is  located  nearby, 
will  the  freezing  process  prove  commercially  practicable.  It 
is  an  expensive,  slow  and  uncertain  process. 

ART.  129.    HYDRAULIC  CAISSONS 

This  type  of  caisson  has  been  used  in  a  few  cases  for  deep 
building  foundations  but  it  is  ill-adapted  to  most  soils.  Where 
sand  predominates  and  no  boulders  are  present  it  may  be  used 
with  success.  The  caisson  consists  of  a  riveted  steel  cylin- 
drical shell,  say  from  5  to  14  feet  in  diameter  and  as  high  as  nec- 
essary. The  lower  edge  is  shod  with  a  hollow  cast-iron  cutting 
edge  of  a  triangular  cross-section,  which  is  perforated  with  many 
holes  forming  special  nozzles.  This  cutting  edge  is  composed 
of  a  number  of  sections,  each  section  having  an  inside  chamber 
independent  of  all  other  sections.  By  means  of  pipes  and  flex- 
ible tubing  these  chambers  are  connected  with  a  force  pump. 
The  material  is  first  excavated  to  ground-water  level,  after 
which  the  caisson  is  placed  in  this  excavation;  the  caisson  is 
then  heavily  weighted  and  water  is  forced  into  the  cutting-edge 
chambers  and  thence  out  through  the  small  nozzles  to  scour  the 
material  from  under  and  around  the  cutting  edge,  thus  causing 
the  caisson  to  sink.  When  the  stratum  on  which  the  caisson 
is  to  rest  is  reached  the  hydraulic  pressure  is  discontinued  and 
the  spoil  is  excavated  from  the  interior  in  the  dry,  after  which  the 
pier  is  built  by  filling  with  concrete.  If  the  caisson  is  bedded 
in  clay  the  excavating  and  pier-building  are  easily  done  in  the 
dry,  but  if  it  rests  on  rock  it  is  often  a  difficult  matter  to  keep 
out  the  water.  This  feature  and  the  risk  of  meeting  boulders 


ART.  129 


HYDRAULIC    CAISSONS 


383 


in  sinking  makes  this  method  of  founding  piers  a  very  uncertain 
one.  This  type  of  caisson  was  used  in  placing  the  foundations 
of  the  Johnson  and  the  Meyer- Jonassen  Buildings,  both  located 
in  New  York  City.  Descriptions  are  given  in  Engineering 
Record,  vol.  32,  page  116;  and  vol.  33,  page  315.  It  appears 
that  the  use  of  this  method  has  been  abandoned. 


CHAPTER  XII 
ORDINARY  BRIDGE  PIERS 

ART.  130.     GENERAL  REQUIREMENTS 

In  selecting  the  site  of  a  bridge  and  arranging  the  piers, 
careful  attention  must  be  given  to  such  matters  as  location  of 
crossing,  position  and  spacing  of  piers  and  abutments,  height 
of  bridge,  required  waterway,  etc.  Where  the  construction 
is  in  new  country  the  location  of  the  bridge  can  usually  be  made 
to  suit  the  engineering  requirements.  These  will  be  best 
satisfied  where  the  width  of  the  river  is  not  great;  however,  it 
should  not  be  located  in  the  narrowest  part  for  there  the  current 
is  apt  to  be  swift  and  the  water  deep  at  times  of  heavy  rains, 
thus  making  the  construction  of  the  substructure  both  difficult 
and  expensive.  On  the  other  hand,  where  the  bridge  is  located 
in  a  built-up  community  it  will  have  to  be  placed  where  it  will 
best  serve  the  needs  of  the  people.  If  it  is  a  highway  structure 
it  will  connect  main  thoroughfares  on  the  two  sides  of  the  river, 
while  a  railroad  structure  has  to  connect  the  rights-of-way. 
Building  new  streets  or  buying  rights-of-way  is  very  expensive 
in  built-up  vicinities  and  will  usually  be  in  excess  of  any  pos- 
sible saving  in  the  cost  of  the  bridge  by  placing  the  latter  in  a 
more  advantageous  position  from  an  engineering  standpoint. 

In  determining  the  number  of  piers  and  their  spacing,  due 
regard  should  be  given  to  the  financial  considerations,  the  navi- 
gation interests,  waterway  requirements,  and  the  Government 
rules  and  regulations. 

The  financial  requirements  are  best  served  by  an  arrangement 
which  makes  the  total  cost  of  the  bridge,  superstructure  plus 
substructure,  a  minimum.  As  the  cost  of  the  superstructure 
varies  approximately  as  the  square  of  the  length  of  a  span  and 
the  cost  of  a  pier  with  its  foundation  is  approximately  a  constant 

384 


ART.  130  GENERAL  REQUIREMENTS  385 

for  fairly  wide  ranges  of  span  length,  there  is  some  length  of 
span  which,  with  its  corresponding  number  of  piers,  will  make 
the  total  cost  of  the  bridge  a  minimum.  For  the  deduction  of 
such  a  formula  see  Art.  9  of  MERRIMAN  &  JACOBY'S  Roofs  and 
Bridges,  Part  III.  This  formula  shows  that  for  minimum 
cost  the  cost  of  one  river  pier  should  equal  the  cost  of  the 
main  and  lateral  trusses  of  one  span.  In  deriving  the  for- 
mula it  was  assumed  that  the  lengths  of  all  spans  are 
approximately  equal. 

Navigation  interests  require  that  the  piers  shall  be  placed  so 
as  to  cause  as  little  danger  and  obstruction  as  possible  to  river 
traffic.  Thus  they  should  be  kept  out  of  the  channel  and  should 
be  spaced  at  considerable  distances  apart. 

The  pier  should  rest  on  a  stable,  unyielding  foundation,  the 
base  of  which  is  well  below  the  frost  line  and  below  the  elevation 
of  any  possible  scouring  action.  Where  rock  or  other  satis- 
factory bearing  material  lies  at  a  depth  not  greater  than  from 
20  to  30  feet  below  water  level,  the  pier  footing  will  usually  be 
placed  directly  on  the  rock  surface,  a  cofferdam  being  used  if 
necessary.  The  material  overlying  the  rock  is  first  removed, 
after  which  the  latter  should  be  leveled  or  stepped  off  and  cleared 
of  all  loose  material  before  placing  the  footing  for  the  pier. 

For  depths  varying  from  20  to  40  feet  or  more  a  pile  founda- 
tion will  usually  prove  the  cheapest.  The  correct  principles  of 
design  for  this  type  of  foundation  are  discussed  in  preceding 
chapters.  For  depths  greater  than  about  40  feet  some  type  of 
caisson  foundation  is  generally  used. 

Shallow  foundations,  corresponding  to  the  spread  footings  so 
much  used  for  buildings,  are  seldom  used  for  bridges.  Up  to 
about  twnety  years  ago,  a  spread  footing  consisting  of  a  timber 
grillage  was  a  common  type  of  foundation  for  bridges.  The 
grillage  consisted  of  a  more  or  less  open  mass  of  timbers  laid 
directly  on  the  gravel  bottom  after  dredging  out  a  few  feet,  and 
extending  to  nearly  low-water  level.  The  grillage  was  built, 
with  courses  alternating  in  direction,  to  a  height  of  a  few  feet 
on  shore,  after  which  it  was  launched,  completed,  towed  to  the 
site  and  sunk  by  filling  the  open  spaces  between  the  timbers 
25 


386 


ORDINARY  BRIDGE    PIERS 


CHAP.  XII 


'^i":i:r.T.vi::i"ii~T 

Cross -Section 


E-  F 


,r 


with  stones,  etc.  The  disadvantage  of  this  type  of  foundation 
lies  in  the  fact  that  it  is  practically  impossible  to  land  the 
grillage  perfectly  level  owing  to  the  great  difficulty  of  preparing 
a  level  foundation  bed.  Another  disadvantage  lies  in  the  danger 
from  scour.  Further  details  relating  to  this  type  of  foundation 

may  be  found  in  an 
article  by  E.  K.  MORSE, 
in  Proceedings  Engineer's 
Society  of  Western  Penn- 
sylvania, Feb.,  1911,  and 
in  FOWLER'S  Sub-aque- 
ous Foundations. 

Fig.  1300  illustrates  an 
interesting  type  of  shallow 
foundation  which  sup- 
ports the  piers  of  the 
Kingshighway  Viaduct, 
St.  Louis,  Mo.  It  con- 
sists of  a  reinforced-con- 
crete  box  open  at  the 
bottom  and  closed  at  the 
top.  The  top  has  a 
thickness  of  4  feet,  while 
the  thickness  of  the  sides 
and  cross  walls  vary  from 

i\  to  3  feet.  It  was  originally  intended  to  found  the  piers  on 
concrete  piles  (shown  in  the  diagram),  but  in  testing  some  of  the 
piles  already  driven  the  soil  was  found  to  be  an  incompressible 
but  perfectly  plastic  clay,  which  would  not  take  the  arch  thrust 
with  a  pile  foundation.  By  using  the  concrete  box  the  clay  was 
confined  to  prevent  flowing  action,  while  the  large  area  of  the 
sides  took  care  of  the  horizontal  thrust. 

ART.  131.     DEFINITIONS 

A  bridge  pier  is  a  structure,  usually  composed  of  masonry, 
which  is  used  to  transmit  the  loads  from  the  bridge  superstruc- 
ture to  the  foundation. 


East 
47-11'- 


- ->! 


EN&.NEWS 

FIG.  i3oa. — Reinforced-concrete  Pier  Footing, 
Viaduct,  St.  Louis,  Mo. 


ART.  131  DEFINITIONS  387 

Some  of  the  common  parts  of  a  bridge  pier  are  the  following: 
BRIDGE  SEAT. — A  block  of  stone  or  concrete  resting  on  the  top 
of  a  pier  to  support  the  pedestal  or  base  plate.  COPING. — The 
top  course  of  the  pier,  usually  projecting  beyond  the  other 
courses.  BELTING  COURSE. — The  course  immediately  below 
the  coping  course.  FOOTING  COURSES. — Those  courses  at  or 
near  the  bottom  of  the  pier,  which  are  wider  than  those  in  the 
main  part  of  the  pier.  BODY. — The  main  part  of  the  pier. 
STARLING. — That  part  of  the  pier  below  high  water,  the  hori- 
zontal section  of  which  lies  outside  of  the  largest  rectangle  that 
can  be  formed  on  the  two  sides  of  the  pier.  STARLING  COPING. 
—The  offset  course  at  about  high  water  which  forms  the  top 
course  of  the  starling.  BATTER. — The  slope  of  the  sides  and 
ends  of  the  pier. 

The  coping  course  serves  to  protect  the  pier  from  the  weather. 
If  made  of  stone  masonry  the  stone  is  of  the  best  quality  and 
cut  to  make  small  joints;  if  of  concrete  a  rich  mixture  is  em- 
ployed. The  top  is  usually  made  with  a  surface  sloping  from 
the  middle  downward  to  the  sides  and  is  often  waterproofed 
with  some  waterproofing  compound,  especially  when  of  con- 
crete. It  is  customary  to  give  the  coping  course  an  offset  of 
from  6  to  1 2  inches  in  order  to  prevent  rain-water  from  dripping 
down  the  sides  and  ends  of  the  pier,  and  also  to  improve  the 
appearance  of  the  pier. 

The  chief  function  of  the  belting  course  is  to  strengthen  the 
coping  offset,  but  it  also  improves  the  appearance  of  the  pier. 
In  special  cases  two  or  three  belting  courses  are  used,  while  at 
other  times  none  are  employed. 

The  function  of  the  footing  course  is  to  distribute  the  load 
over  a  larger  area  than  the  base  of  the  body  of  the  pier.  Unless 
reinforced  the  slope  of  the  footing  should  not  be  over  30  degrees 
with  the  vertical;  where  reinforced  the  slope  may  be  anything 
consistent  with  safe  stresses  in  the  steel  and  concrete  as  deter- 
mined when  considering  the  projecting  footing  courses  to  act  as 
a  cantilever  beam. 

As  explained  in  Art.  132  the  function  of  the  starling  is  .to  pass 
the  water  with  the  least  possible  disturbance,  for  then  there  will 


388  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

be  the  least  pressure  against  the  pier  due  to  current,  ice,  and 
drift,  less  danger  to  navigation  from  eddies,  and  less  danger 
from  .under-scouring. 


ART.  132.     FORM  AND  DIMENSIONS 

The  two  primary  requirements  of  bridge  piers  are:  First,  to 
transmit  the  load  from  the  superstructure  to  the  foundation; 
and  second,  to  disturb  the  natural  movement  of  the  water  as 
little  as  possible.  Naturally  a  minimum  capitalized  cost  should 
also  be  sought.  As  the  load  from  the  superstructure  is  applied 
on  the  pier  at  two  points,  at  a  distance  apart  equal  to  the  width 
of  the  trusses  or  girders  center  to  center,  the  most  economical 
way  of  satisfying  the  first  requirement  is  the  employment  of 
two  cylinders,  one  under  each  load,  as  described  in  Art.  138. 
On  the  other  hand,  the  second  requirement  is  best  served  with  a 
form  resembling  a  ship,  modified  to  increase  the  stability  of  the 
pier  against  floating  ice,  debris,  etc.,  and  to  make  the  con- 
struction cheaper.  The  shape  generally  used  is  that  of  a  rec- 
tangle with  triangles  or  segments  of  circles  at  both  upstream  and 
downstream  ends,  or  at  only  the  upstream  end.  The  advan- 
tage of  having  starlings  at  both  ends  is  that  the  foundation 
becomes  symmetrical  with  the  loads,  thus  avoiding  an  uneven 
distribution  of  pressure  on  the  foundation  bed;  eddying  on  the 
downstream  end  of  the  pier  is  also  reduced.  Starlings  are 
necessary  only  below  high  water. 

The  triangular  nose,  usually  made  with  a  go-degree  angle  at 
the  vertex,  has  the  advantage  over  the  curved  nose  in  cheapness 
of  construction,  but  experiments  show  that  it  offers  more  resist- 
ance to  the  passage  of  water.  Experiments  made  by  CRESY 
indicate  the  value  of  different  shapes  of  piers  in  passing  the  water 
to  be  in  the  following  order:  First,  elliptical  horizontal  sections; 
second,  rectangular  body  with  starlings  formed  by  two  circular 
arcs,  tangent  to  the  sides  and  described  on  the  sides  of  an 
equilateral  triangle;  third,  rectangular  body  with  triangular 
starlings,  the  angle  at  the  nose  being  60  degrees;  fourth,  rec- 
tangular body  with  semicircular  starlings;  fifth,  rectangular 


ART.  132  FORM   AND  DIMENSIONS  389 

body  with  triangular  starlings,  the  angle  at  the  nose  being  90 
degrees;  and  sixth,  rectangular  body  without  starlings.  Those 
forms  which  pass  the  current  best  lack  strength  and  massiveness 
in  their  starlings.  Where  used  in  swift  streams  filled  with  ice 
in  winter  the  starlings  are  heavily  reinforced  with  old  rails  or 
structural  shapes.  For  an  example  of  such  reinforcment  the 
reader  is  referred  to  Art.  134. 

Where  segments  of  circles  are  used  the  curves  are  tangent  to 
the  sides  of  the  pier  and  have  radii  somewhat  greater  than  half 
the  thickness  of  the  pier  to  give  a  pointed  end.  A  value  used  on 
many  piers  and  recommended  by  G.  S.  MORISON  is  three-quar- 
ters the  width  of  the  pier.  Above  high  water  the  ends  of  the 
pier  may  be  made  square  but  a  much  better  appearance  is 
secured  when  a  semicircular  form  is  used.  A  combination  of 
the  straight  and  circular  nose  is  sometimes  adopted  and  is  illus- 
trated in  Art.  135.  Where  the  pier  extends  a  considerable  dis- 
tance above  high  water  it  is  customary  to  reduce  the  section 
somewhat  above  that  elevation.  More  complete  details  of  this 
are  given  in  Art.  134. 

DIMENSIONS  OF  BRIDGE  PIERS. — The  dimensions  of  ordi- 
nary bridge  piers  depend  upon  the  load  to  be  supported,  class  of 
superstructure,  height  of  pier,  type  of  foundation,  and  magni- 
tude of  lateral  forces  to  be  resisted. 

The  dimensions  of  the  top  of  the  pier  depend  on  the  distance 
between  trusses  or  girders,  plus  a  certain  amount  necessary  to 
prevent  the  load  from  the  pedestals  approaching  too  closely  the 
edges  of  the  pier,  under  the  coping.  GREINER  specifies1  that 
the  width  shall  not  be  less  than  4  feet,  nor  less  than  that 
required  for  the  bearings  of  the  superstructure  plus  i  foot,  nor 
less  than  that  required  to  give  the  required  stability.  The  ques- 
tion of  stability  is  discussed  in  Art.  136.  He  also  specifies 
that  the  length  under  the  coping  shall  not  be  less  than  the  dis- 
tance out  to  out  of  superstructure  bearings  plus  one  and  one- 
quarter  times  the  width  of  the  pier. 

For  electric  railway  bridges  C.  C.  SCHNEIDER,  in  an  article  in 
the  Street  Railway  Journal,  Sept.  15,  1906,  specifies  that  the 

1  General  Specifications  for  Bridges,  Part  III,  by  J.  E.  GREINER. 


390 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


thickness  of  the  pier  under  the  coping  should  not  be  less  than  4 
feet.  "The  usual  practice  is  to  have  the  masonry  on  top 
(under  coping)  project  3  inches  in  the  direction  of  the  thickness 


FIG.   1320. — Outline  of  Standard  Concrete  Pier. 

of  the  pier  and  at  least  6  inches  in  the  direction  of  the  length  of 
the  pier  beyond  the  edges  of  the  base  plate.''  For  piers  support- 
ing two  spans  of  approximately  the  same  length,  Table  No.  13  20, 


To  obtain  volume -Follow horizon/a/ 
line  height  to  an  intersecfion  with 


curved  line  indicating  w/dtn,  /hen 
vertically  up  or  down  to  intersect. 


tic-ally  up  or  down  to  intersection 
with  curved  line  indicating  length, 
thence  horizontally  across  toscale 
indicating  vo/ume 


1200 


FIG.  1326. — Diagram  for  Cubature  of  Concrete  Piers. 

taken  from  the  article  just  noted,  gives  the  approximate  mini- 
mum dimensions  for  electric  railway  bridge  piers. 

Fig.  13  20  shows  the  standard  form  of  pier  for  the  Harriman 


ART.  132  FORM   AND  DIMENSIONS  391 

Lines,  while  Tables  Nos.  13  ib  and  c  respectively  give  the  lengths 
and  widths  under  copings  for  various  types  of  superstructures. 
Fig.  13  ib  gives  the  volume  of  masonry  in  this  type  of  pier  for 
various  heights,  lengths  and  widths. 

The  coping  course  usually  has  a  thickness  varying  from  i 
to  2\  feet,  and  an  offset  depending  on  the  thickness.  When 
concrete  is  used  GREINER  specifies  that  "  copings  shall  not  have 
a  less  depth  than  i  foot  nor  less  than  one- sixth  of  the  thickness 
of  the  stem  measured  under  coping.  They  shall  project  over 
the  faces  of  the  stem  to  an  extent  equal  to  about  one-third 
their  depth.  This  projection  shall  be  neatly  moulded  on 
the  bottom  and  champ fered  on  the  top  and  have  all  corners 
rounded."  COOPER  specifies  that  lathe  coping  shall  extend  at 
least  3  inches  all  around,  but  not  more  than  one-third  of  its 
thickness."  This  specification  is  for  highway  and  electric 
railway  bridges.  The  specifications  for  the  Harriman  Lines  call 
for  a  4-inch  projection  of  coping  for  concrete  piers  and  for  ma- 
sonry piers  10  feet  and  under  in  height,  and  a  6-inch  projection 
for  masonry  piers  over  10  feet  high.  In  the  Thebes  bridge 
piers,  Fig.  134^,  the  thickness  of  the  stone  masonry  coping  is 
27  inches  and  the  projection  24  inches.  The  belting  course  not 
only  improves  the  appearance  of  the  pier  but  helps  to  secure 
a  greater  projection  of  the  coping  course.  Its  dimensions  and 
form  vary. 

As  noted  in  a  previous  article  a  single  or  double  belting  may 
be  employed  or  the  same  may  be  dispensed  with  altogether. 
When  used  it  is  usually  made  of  about  the  same  or  somewhat 
less  thickness  as  the  coping  course  and  its  projection  beyond  the 
stem  of  the  pier  is  closely  equal  to  the  projection  of  the  coping 
course  beyond  the  belting  course.  As  to  whether  a  double 
belting  course  is  preferable  to  a  single  one  in  any  given  case  will 
depend  on*the  desired  total  off-set  of  the  coping  course  with 
reference  to  the  stem  of  the  pier.  In  the  following  articles  a 
number  of  examples  of  piers  are  illustrated  which  show  clearly 
their  belting  courses. 

1  General  Specifications  for  Foundations  and  Substructures  of  Highway  and 
Electric  Railway  Bridges,  by  THEODORE  COOPER. 


392 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


TABLE  NO.  1320 
APPROXIMATE  MINIMUM  DIMENSIONS  or  ELECTRIC  RAILWAY  BRIDGE    PIERS 


Thickness  of  pier  under  coping 

Span 

Class  A 

Class  B 

Class  C 

S.  T.             D.  T. 

S.  T        |        D.  T. 

S.  T. 

D.  T. 

25 

4-0 

4-0 

4-0 

4-0 

4-  0 

4-0 

50 

4-0 

5-3 

4-0 

4-0 

4-  o 

4-0 

75 

4-6 

6-0 

4-0 

4-6 

4-  o 

4-0 

100 

5-o 

6-6 

4-0 

5-o 

4-  o 

4-0 

125 

5-4 

7-0 

4-0 

5-4 

4-  o 

4-4 

150 

5-8 

7-6 

4-3 

5-8 

4-  o 

4-8 

175 

6-0 

8-0 

4-6 

6-0 

4-  o 

5-o 

200 

6-4 

8-6 

4-9 

6-4 

4-  o 

5-4 

250 

7-0 

9-6 

5-3 

7-0 

4-  6 

6-0 

300 

7-8 

10-6 

5-9 

7-8 

4-10 

6-6 

350 

8-4 

1  1-4 

6-2 

8-4 

5-  2 

7-0 

400 

9-0 

I2-O 

6-6 

9-0 

5-  6 

7-6 

Length  of  pier  under  coping  =  distance  center  to  center  of 
trusses  +  figures  below 

Class  A 

Class  B 

Class  C 

S.  T.      |        D.  T. 

S.  T.       |       D.  T. 

S.  T. 

D.  T. 

So 

3-6 

4-0 

3-6 

3-6 

3-6 

3-6 

IOO 

4-0 

5-o 

3-6 

4-0 

3-6 

3-6 

ISO 

4-6 

5-6 

4-0 

4-6 

3-6 

4-0 

200 

5-o 

6-0 

4-0 

5-o 

3-6 

4-6 

250 

5-o 

6-6 

4-6 

5-o 

4-  o 

4-6 

300 

5-6 

7-0 

4-6 

5-6 

4-  o 

5-o 

350 

6-0 

7-6 

4-6 

6-0 

4-  6 

5-o 

400 

6-0 

7-6 

5-o 

6-0 

4-    6 

5-6 

Note:  All  values  are  expressed  in  feet  and  inches.  S.  T.  =  single  track; 
D.  T.  =  double  track.  Class  A,  heavy  traffic;  Class  B,  medium  traffic;  Class  C, 
light  traffic. 

TABLE  NO.  13  2b 

LENGTH   UNDER   COPING   OF   CONCRETE   BRIDGE   PIERS 
HARRIMAN  LINES'    STANDARD,  1906 


Deck 

plate  girders 

Through  riveted 

trusses 

Span... 

20 

30 

40 

50 

60 

70 

80 

90 

IOO 

iooi 

IIOJ 

125 

140  j  150 

Length  . 

8-4 

9-2 

9-0 

9-2 

10-0 

II-O 

I  I-O  1  2-2 

12-2 

20-01  20-0  20-0 

20-820-8 

Through  pin  trusses 

||                                  Through  plate  girders 

Span  .  .  . 

150 

1  60 

1  80 

2OO 

30 

40 

50 

60 

I    70 

80 

90 

IOO 

Length.  21-2  21-2  21-421-4 

16-8  17-10  1  8-2  19-0  19-10 

19-6 

19-8 

19-10 

Note:  Length  of  pier  to  correspond  to  length  given  in  table  for  the  longer  span 
All  dimensions  are  expressed  in  feet  and  inches. 


ART.  132 


FORM  AND   DIMENSIONS 


393 


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394  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

The  sides  of  the  body  or  stem  of  the  pier  are  invariably  given 
a  batter  of  either  i  in  24  or  i  in  12.  Above  high  water  the 
ends  are  also  given  this  batter.  The  former  value  is  more  com- 
monly used  for  high  piers  and  the  latter  for  low  piers.  Either 
gives  a  pier  of  good  appearance  and  will  usually  furnish  ade- 
quate stability  and  a  base  of  sufficient  size. 

The  footing  courses  serve  to  transfer  the  load  from  the  body 
of  the  pier  to  the  foundation  and  for  this  reason  they  are 
given  a  larger  horizontal  section  than  the  base  of  the  body  of 
the  pier. 

GREINER  specifies  the  following  in  regard  to  their  dimen- 
sions: "The  upper  surface  of  the  upper  footing  course  shall  not 
project  more  than  i  foot  beyond  any  face  of  the  stem.  .  .  . 
The  depth  of  any  footing  course  shall  not  be  less  than  2  feet 
and  the  courses  may  be  stepped  off  at  an  angle  of  about  30 
degrees  with  the  vertical  or  have  a  uniform  batter  of  the  same 
amount.  When  constructed  on  pile  foundations  the  footings 
shall  encase  the  piles  to  a  depth  of  at  least  6  inches,  and  the 
distance  from  the  center  of  any  pile  to  the  outside  face  of 
the  footing  shall  not  be  less  than  i|  feet." 

ART.  133.    MATERIALS  AND  CONSTRUCTION 

Previous  to  about  1880  it  was  the  universal  rule  to  build  piers 
entirely  of  stone  masonry,  while  at  the  present  time  most  piers 
are  built  either  entirely  of  concrete  or  of  a  concrete  hearting  and 
stone  facing.  Three  conditions  have  brought  about  this  change  : 
First,  the  decrease  in  the  cost  of  cement;  second,  the  increase 
in  the  strength  and  the  greater  reliability  of  cement  and  con- 
crete; and  third,  the  increased  cost  of  cut  stone,  due  to  the 
labor  factor. 

Among  the  earliest  of  the  all-concrete  piers  in  this  country 
were  those  used  for  a  bridge  across  the  Medina  River,  i8|  miles 
west  of  San  Antonio,  Texas,  built  in  1881.  In  Nova  Scotia 
they  were  first  used  in  1883.  In  both  of  these  instances  concrete 
was  used  because  of  the  absence  of  good  stone  in  the  vicinity 
and  the  high  cost  of  transportation.  In  Europe  the  all-concrete 


ART.  133  MATERIALS   AND   CONSTRUCTION  395 

pier  was  used  somewhat  earlier  than  the  above  dates.  For  some 
years  after  its  introduction 'the  development  of  the  all-concrete 
pier  was  slow.  In  an  address  delivered  in  1899,  G.  S.  MORISON 
said:  *" Prejudices  have  been  raised  against  it  (concrete) 
through  inferior  work  done  in  this  country  when  it  was  first 
introduced,  but  it  is  within  the  limits  of  possibilities  that  an 
artificial  stone  can  be  made  in  this  way  which  will  be  as  good 
and  as  durable  as  the  natural  stones  which  are  commonly  used; 
when  this  is  accomplished  the  advantages  of  a  truly  monolithic 
construction  will  make  concrete  the  best  building  material,  and, 
except  for  the  facings  of  monumental  works,  where  nothing 
can  take  the  place  of  the  finest  stone  from  nature's  laboratory, 
it  may  be  universally  used." 

Considering  the  stone-masonry  pier  as  exemplified  in  many 
large  bridges  built  by  G.  S.  MORISON,  the  facing  courses  are 
mostly  limestone  ashlar,  with  granite  ashlar  for  the  upstream 
nose  stones  for  all  courses  between  high  and  low  water.  The 
backing  is  composed  of  limestone  rubble,  in  some  cases  with, 
and  in  other  cases  without,  coursed  joints.  For  the  Belle- 
fontaine  bridge,  built  in  1892,  it  was  specified  that  the  backing 
stones  should  have  the  same  thickness  as  the  face  stones  and 
that  the  spaces  between  the  large  stones  of  the  backing  should 
not  occupy  more  than  one-fifth  of  the  volume  of  the  pier  inside 
the  face  stones,  and  that  these  spaces  should  be  filled  with  good 
rubble  masonry. 

The  piers  for  the  Merchants  bridge  across  the  Mississippi 
River  at  St.  Louis,  built  in  1889,  were  among  the  early  large 
piers  to  have  concrete  backing.  Here  the  coping  course,  the 
three  courses  below  this,  and  the  starling  coping  course  were  all 
of  stone  masonry,  the  remainder  of  the  backing  being  concrete. 
Fig.  1330  shows  the  details  of  the  stone  masonry  for  the  starling 
coping  for  piers  I  and  IV. 

For  complete  and  up-to-date  specifications  for  stone  masonry 
the  reader  is  referred  to  the  Manual  of  the  American  Railway 
Engineering  Association. 

The  advantage  of  concrete  over  stone  masonry  lies  in  its 

Engineering  Record,  vol.  39,  page  497,  April  29,  1899. 


396 


ORDINARY  BRIDGE    PIERS 


CHAP.  XII 


lesser  cost.  Although  its  compressive  strength  is  somewhat  less 
than  that  of  first-class  stone  masonry,  yet  on  account  of  its 
monolithic  character,  most  engineers  agree  that  it  is  the  more 
suitable  material,  except  possibly  for  the  facing  of  the  pier. 
Mixtures  of  1-2^-5  or  1-3-6  proportions  are  usually  adopted  for 
the  hearting,  and  a  richer  mixture  for  the  coping  course. 

There  are  some  advantages,  however,  in  using  a  facing  of 
stone  masonry,  among  these  being  the  saving  in  the  expense  of 


t    I 


Downstream 
End 


Section  at  A.  Section  atB.          SectionatC.     Section  at  D. 

FIG.   i33a. — Starling  Coping  Course  for  Pier  IV,   Merchant's   Bridge,   St.   Louis. 


Isometric  View 

of  Stone  12. 


forms,  the  more  rapid  rate  of  construction  possible,  the  more 
attractive  appearance  of  the  pier,  and  the  elimination  of  sur- 
face cracks.  These  surface  cracks,  almost  always  present  in 
plain  concrete  piers,  are  due  to  the  expansion  and  contrac- 
tion, caused  by  temperature  changes,  of  the  outer  layer  of 
concrete. 

Where  a  stone-masonry  facing  and  concrete  backing  are  used 
for  piers  bearing  very  heavy  loads  the  facing  stones  should  be 


ART.  133  MATERIAL  AND  CONSTRUCTION  397 

tied  in  with  rods,  as  shown  in  Fig.  134^.  Where  the  all- 
concrete  pier  is  used  it  is  advisable  to  place  reinforcing  rods 
near  the  surface.  This  reinforcement  will  prevent  the  occur- 
rence of,  or  at  least  decrease  the  size  of,  the  cracks  noted 
above,  and  will  also  add  an  element  of  safety  by  taking  any 
tensile  stresses  in  the  concrete.  Reinforcement  in  horizontal 
planes  under  the  coping  and  above  the  bottom  of  the  footing 
serves  to  carry  the  loads  more  uniformly  into  the  pier  and 
foundation. 

GREINER'S  Specifications  state :  "  All  faces  of  the  stems  above 
the -footing  courses,  unless  otherwise  specified,  shall  have 
surface  reinforcement  for  bonding  the  concrete  composed  of  a 
network  of  round  or  deformed  bars  with  meshes  of  about  i  foot 
vertical  by  2  feet  horizontal,  the  weight  of  metal  being  not  less 
than  2\  pounds  for  railway  and  i|  pounds  for  other  bridges  for 
each  square  foot  of  surface  reinforced.  This  network  shall  be 
embedded  in  the  concrete  to  a  depth  of  2  inches,  the  horizontal 
rods  being  on  the  outside  of  the  vertical  rods  and  wired  thereto. 
The  vertical  rods  shall  extend  into  the  footings  to  an  extent 
necessary  for  proper  bond.  The  faces  of  copings  shall  have 
continuous  surface  reinforcement,  of  the  same  weight  per  square 
foot  of  surface,  as  provided  for  stems.  .  .  . 

"The  lower  footing  course  when  on  pile  foundations  shall  have 
horizontal  reinforcement  for  bonding  the  concrete  composed  of 
a  layer  of  rods  forming  a  network  placed  about  6  inches  above 
the  bed  or  placed  around  and  between  the  embedded  part  of 
the  piles,  the  weight  of  metal  per  square  foot  of  network  being 
not  less  than  3  pounds  for  railway  and  2  pounds  for  other 
bridges.  The  stem  shall  have  similar  layers  of  horizontal 
reinforcement  of  the  same  weight  per  square  foot  as  provided 
for  surface  reinforcement,  embedded  i  foot  below  the  coping, 
i  foot  above  the  footing  course  and  at  intermediate  points  at 
intervals  not  exceeding  20  feet.  A  similar  network  shall  be 
embedded  in  the  coping  about  2  inches  below  its  upper  surface. 
The  meshes  in  the  horizontal  layers  of  network  shall  be 
preferably  square." 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


ART.  134.    EXAMPLES  OF  SOLID  PIERS 

Fig.  1340  illustrates  a  simple  form  of  the  solid  all-concrete 
pier  used  by  the  Western  Maryland  Railroad.  The  dimensions 
are  given  in  the  diagram.  luThe  upstream  end  of  the  pier  is 


-.^  Boise  of  Rail. 


Cross-  Section. 


Side    Elevation. 


FIG.   1340. — Concrete  Bridge  Pier,  Fourth  Crossing  of  Potomac   River,   Western 

Maryland  Railroad. 

built  with  its  sides  at  a  45 -degree  angle  with  its  transverse  axis 
to  form  a  cutwater  end,  the  nose  of  which  extends  3  feet  3 
inches  beyond  the  corner  of  the  pier  at  the  lower  edge  of  the  cop- 
ing. This  nose  was  molded  to  a  circle  by  inserting  within  the 
forms  a  strip  of  No.  16  iron,  9  inches  wide,  bent  to  a  6-inch 
1  Engineering  Record,  vol.  51,  page  304,  March  n,  1905. 


ART.  134 


EXAMPLES    OF    SOLID    PIERS 


399 


radius.  It  is  held  in  place  by  i-inch  bolts,  9  inches  long,  ex- 
tending into  the  concrete.  They  have  a  welded  head  on  the 
end  outside  the  plate,  and  a  head  and  a  2-inch  washer  on.  the 
end  in  the  concrete." 

A  good  example  of  the  all-concrete  pier  with  reinforcement 
near  the  outer  surface  is  shown  in  Fig.  1346,  which  illustrates 
one  of  the  piers  for  the  Gilbertsville  bridge.  The  bottom  of 
the  footing  and  top  of  the  coping  are  also  reinforced. 


El.  109. 3' 


-IQ'O 
l;3:6  Concrete.        End  Elevation 


Cross-  Section 


S  Boise  Cbrsting 
Half  Ran.  Half  Pile  P/an. 

FIG.   1346. — General  Dimensions  of  Piers  of  Illinois  Central  Railroad  Bridge  over 
Tennessee   River,    Gilbertsville,    Ky. 

Fig.  i34<;  shows  the  sectional  elevation  and  plans  of  various 
courses  of  the  part  above  high  water  of  Pier  3  of  the  Beaver 
bridge  of  the  Pittsburgh  &  Lake  Erie  Railroad.  The  facing 
is  of  ashlar  sandstone  with  1-3-5  concrete  backing.  As  shown 
in  the  illustrations  the  facing  was  securely  tied  to  the  backing 
by  ij-inch  rods  running  both  lengthwise  and  crosswise.  Extra 
rods  were  used  to  reinforce  the  hearting.  Contrary  to  the  usual 
practice  in  large  stone-faced  piers  a  stone  coping  course  was  not 


400 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


used,  a  ring  around  the  outside  being  of  stone  and  the  rest 
concrete.  The  shoe  grillage  of  I-beams  which  takes  the  load 
from  the  superstructure  and  distributes  it  over  an  area  of  240 
square  feet  on  the  pier  rests  on  and  is  supported  by  a  1-2-4 
mixture  of  concrete  (the  darker  portion  in  the  illustration). 
To  waterproof  the  top  of  the  pier  a  granolithic  roof  about  3 


FIG.   134^. — Cross-section  and  Plans  of  Pier  3,  Pittsburgh  &  Lake    Erie   Railway 
Bridge  over  Ohio  River,  Beaver,  Pa. 

inches  thick  was  placed  over  the  entire  top.  The  total  load 
from  the  superstructure  is  12  ooo  tons  and  the  pressure  on 
the  masonry  under  the  grillage  is  about  25  tons  per  square 
foot. 

Fig.  1346?  shows  a  common  type  where  the  pier  is  offset  all 
around  at  the  high-water  line  and  has  a  starling  coping  course 
projecting  on  both  sides  and  ends. 

Pier  2  of  the  Thebes  bridge  of  the  Illinois  Central  Railroad 
is  a  type  of  pier  used  in  many  large  structures  across  the  Miss- 


£ 


f 


FIG.   1340. — Pier  2  of  Cantilever  Bridge  over  the  Mississippi  River  at  Thebes,  111. 
Designed  by  Noble  and  Modjeski.     April  i,  1905. 


FIG.   i34/. — Pier  3  of  McKinley  Bridge  over  the  Mississippi  River  at  St.  Louis, 
Mo.,  Showing  Starling  with  Conical  Top.     May  16,  1909. 

(Facing  Fig.  134*.) 


FIG.  134*'. — A  Pier  of  the  Victoria,  or  Grand  Trunk  Railroad  Bridge  over  the 
St.  Lawrence  River  at  Montreal,  Ont.  Built  in  1858.  The  nose  of  the  ice-breaker 
has  an  inclination  of  about  43  degrees,  and  is  protected  by  iron  plates.  See 
Engineering  Record,  vol.  38,  page  444  and  466,  Oct.  22  and  29,  1898. 


ART.  134 


EXAMPLES   OF   SOLID   PIERS 


401 


issippi  and  Missouri  Rivers.  As  shown  in  Fig.  1340,  it  is  a  very 
simple  form  of  pier  and  in  its  simplicity  lies  its  beauty.  The 
sides  are  parallel  and  the  ends  are  formed  by  two  circular  arcs 
meeting.  Above  high  water  the  ends  are  semicircular.  The 
coping  projects  2  feet  beyond  the  pier  and  the  projection  is 


M/Hflqr          I 


'J — 49' — .-- 

t"*1 


This  Surface  fine  \ 
Pointed  on  both  \ 


Ends  of  Pier-.. 

I 


n 

•a* 


- 1 


62  '/Ok" 


End   Elevation, 


Side    Elevation 


on  Up 
nd 


*i 


Caisson 

Plan. 

FIG.   i34g. — General  Dimensions  of  Pier  3   of  the  McKinley  Bridge. 

divided  between  the  coping  and  the  belting  course  below.  The 
starling  coping  covers  the  starling  only.  The  pier  has  a  batter 
of  i  in  24. 

Another  bridge  having  piers  of  about  the  same  form  as  that 
just  described  is  the  McKinley  bridge  at  St.  Louis.     The  most 
26 


402 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


notable  difference  between  the  piers  of  the  McKinley  and  Thebes 
bridges  is  in  the  treatment  of  the  top  of  the  starling.  As  shown 
in  Fig.  i34/  and  g,  the  starling  coping  in  the  former  bridge 
is  dispensed  with  and  the  top  of  the  starling  finished  with  a 
conical  surface. 

For  the  McKinley  bridge  piers  the  facing  is  of  limestone, 
with  the  exception  of  the  bridge  seats  and  the  upstream  nose 
stones  above  the  river  bed,  which  are  of  granite.  The  hearting 
is  of  concrete  with  the  exception  of  the  three  courses  below  the 
coping,  which  are  backed  with  limestone  masonry.  luThe 


Side    Elevation^j 

R- /sisfe'-.-yl 


End   Elevation 


Section 


Plan 

FIG.   i34/z. — Pier   with    Ice-breaking   Cutwater.     Flag   Point    Bridge   of   Copper 
River  &   Northwestern   Railway,   Alaska. 

curved  surfaces  of  the  upstream  starlings  are  close  pointed  to 
J-inch  projection.  The  exposed  surfaces  of  the  main  copings 
and  the  projecting  bottom  beds  of  the  belting  courses  are  planed. 
A  4-inch  draft  line  is  cut  along  the  lower  edges  of  the  belting 
courses  and  on  each  side  of  the  vertical  angles  of  the  down- 
stream starlings.  All  other  stones  are  quarry  faced,  with  pro- 
jections not  exceeding  3  inches." 

The  piers  of  the  McKinley  bridge  were  designed  by  RALPH 

1  Engineering  News,  vol.  63,  page  9,  Jan.  6,  1910. 


ART.  135 


EXAMPLES    OF   HOLLOW   PIERS 


403 


MODJESKI,  and  those  of  the  Thebes  bridge  by  ALFRED 
NOBLE  and  RALPH  MODJESKI.  The  piers  for  both  of  these 
bridges  resemble  closely  the  standard  type  designed  by 
GEORGE  S.  MORISON. 

Fi^.  134/5  illustrates  the  pier  of  a  bridge  across  Copper  River, 
Alaska,  built  to  withstand  very  heavy  ice  pressure.  The  cut 
water  has  a  heavy  slope  to  lift  as  well  as  to  cut  and  divert  the 
ice,  and  is  heavily  reinforced  with  old  track  rails.  The  sides 
are  also  reinforced  with  rails. 

Fig.  1347  illustrates  the  steel  plate  protection  for  the  nose  of 
a  pier  of  the  Spokane  bridge  of  the  Inland  Empire  System. 


'^Strap  Anchors,  18  "lonq;  2±  "wide 


(  Nut  End  of  at  I  Bo  Irs  1vbe 

inside.) 


FIG.   134;. — Section  of  Steel  Nose  of  Pier. 

The  steel  plates  were  \  inch  thick  and  5  feet  8|  inches  wide  on 
each  side  of  the  vertex  and  extended  from  the  river  bottom  to 
above  high  water.  They  were  anchored  to  the  pier  byj-inch 
Z-shaped  straps  18  inches  long  and  spaced  18  inches  apart, 
staggered  on  the  nose.  At  the  vertex  the  plates  were  reinforced 
with  a  4X4X|-inch  angle. 

ART.  135.'    EXAMPLES  OF  HOLLOW  PIERS 

In  the  solid  bridge  pier  a  considerable  part  of  the  hearting 
near  the  top  of  the  pier  and  between  the  pedestal  bearings  takes 
but  little  load.  In  other  words,  the  pier  acts  more  or  less  like  a 
double- cylinder  pier,  the  part  directly  under  the  bearings  acting 
somewhat  as  independent  legs  to  carry  the  load,  the  remainder 


404 


ORDINARY  BRIDGE   PIERS 


CHAP.  XII 


acting  chiefly  as  a  bracing  system.  For  this  reason  a  consider- 
able amount  of  concrete  may  be  saved  with  but  small  loss  of 
strength  by  making  the  pier  more  or  less  hollow.  However, 
when  this  is  done  the  remaining  concrete  should  be  well  rein- 


FIG    i35#- — Channel  Piers  of  the  Municipal  Bridge  over  the  Mississippi  River, 
St.  Louis,  Mo. 

forced.     It  is  not  advisable  in  all  cases  to  dispense  with  any  of 

the  filling,  for  massiveness  or  weight  tends  to  reduce  vibration. 

The  hollow  pier  is  a  compromise  between  the  solid  and  the 

cylinder  pier;  it  is  less  expensive  than  the   former  but  has 


FIG.  1456. — Northern  Pacific  Railway  Bridge  over  Heart  River  at  the  Fourth 
Crossing,  4  miles  west  of  Mandan,  North  Dakota,  Showing  Abutments  and  Paved 
Protection  of  Embankments.  Completed  in  1905. 


tf 

I 

•d 


ART.  135 


EXAMPLES   OF   HOLLOW   PIERS 


405 


somewhat  less  stability  and  rigidity;  it  is  more  expensive 
than  the  latter  but  is  far  more  stable  and  makes  a  more 
attractive  substructure. 

The  river  piers  of  the  Municipal  bridge  across  the  Mississippi 
River  at '  St.  Louis,  Mo., 
illustrate  the  hollow  type  of 
pier.  As  shown  in  Figs.  13 50 
and  b,  the  part  above  high 
water  consists  of  a  tall  bat- 
tered shaft  with  a  large  hol- 
low interior  space,  virtually 
forming  two  independent 
shafts  braced  together  with 
a  well  reinforced  arch  at  the 
top  and  walls  of  masonry  on 
the  sides,  the  latter  also  ser- 
ving to  give  it  the  appear- 
ance of  a  solid  pier.  There 
is  a  hollow  space  of  less  size 
below  high  water.  This  pier 
is  also  of  interest  on  account 
of  the  shape  of  cutwater 
which,  as  shown  in  the  plan 
view,  Fig.  13 50,  is  a  combi- 
nation of  the  straight  and 
curved  types  for  the  upstream 
end  and  semicircular  for  the 
downstream  end.  The  con- 
tract price  for  these  piers 
was  $9.50  per  cubic  yard 
from  the  top  of  the  crib  to 
the  coping,  and  $1.90  per 
cubic  foot  for  coping  and 
bridge  seats. 

A  hollow  pier  resting  on  a  pile  foundation  and  supporting 
reinforced-concrete  slabs  is  illustrated  in  Fig.  13  5^.  The  con- 
crete for  the  footings  was  a  1-2-4  mixture  while  that  for  the  pier 


406 


ORDINARY  BRIDGE    PIERS 


CHAP.  XII 


shaft  was  a  1-25-5  mixture.     In  all,  186  piers  of  this  type  were 
used  on  two  bridges  of  the  Pennsylvania  Railroad. 

The  piers  of  the  Sparkman  Street  bridge,  Nashville,  Tenn., 
are  shown  in  Fig.  135  d.  l  "They  consist  of  two  concrete  towers 
extending  from  bridge  seat  to  footing  course,  and  battered  on 
all  sides  J  inch  to  i  foot,  being  braced  together  by  a  reinforced- 


holes  for  Dowels 


*'• 


I^^^W^il 


_ 

A  n  o  n  n  n  n  r"!  n  n  •": r !  ri  n  n  n  si  n 


FIG.   135^. — Piers  for  Bush  and  Gunpowder  River  Bridges 

concrete  arch  and  corbeled  coping  course  at  the  top,  and  by 
reinforced  side  curtain  walls  from  the  footing  course  up  to  the 
high-water  line.  The  curtain  walls  are  2  feet  thick  at  the  top, 
carried  down  plumb  on  the  inside,  and  battering  with  the 
towers  on  the  outside.  The  walls  are  reinforced  with  a  heavy 
meshed  fabric  placed  near  both  inside  and  outside  faces, 
this  fabric  extending  also  entirely  around  the  towers  up  to  the 
top  of  the  curtain  walls." 

1  Engineering  News,  vol.  26,  page  576,  Nov.  25,  1909. 


ART.  135 


EXAMPLES    OF   HOLLOW  PIERS 


407 


Probably  the  boldest  example  of  the  hollow  bridge  pier  is  that 
for  a  bridge  across  the  Willamette  River  near  Portland,  Ore., 
which  is  illustrated  in  Fig.  13 50.  The  bottom  10  feet  of  the  pier 
is  of  solid  concrete,  while  above  this  it  consists  of  a  reinforced- 


*H        *>r     r 
r<  -1  -    -40CfoC. 


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HUH  r^ 


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<  5J'2'~-  -> 

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Y-  /•• 

*g 

% 

j 

«t 

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s 

1 

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i 

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-r-i 

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4rrTT 

Detail   of 

Coping  and  Belt, 

Enlarged. 


-  20 


Section  A-B 


•72' 


LHfc    MEW&. 

Plan. 

FIG    135 d. — Typical  Channel  Pier,  Sparkman  Street  Bridge;  Nashville,  Tenn. 
Arched  above  and  hollow  below  starling  coping  course. 

concrete  shell  and  reinforced-concrete  columns,  the  latter  carry- 
ing directly  the  loads  from  the  superstructure.     The  hollow 
>art  is  braced  by  horizontal  reinforced-concrete  diaphragms. 


408 


ORDINARY  BRIDGE   PIERS 

c/ffe  Seerf 


CHAP.  XII 


Longitudinal  and  Transverse  sections. 


2" Bars 
c  foe  top 
art  of  Jbotfotn 


Plan  of  Diaphragm  No.   i. 

FIG.   1350. — ^Upper   Part   of   Tall    Reinforced-concrete   Pier,    Oregon- Washington 
Railroad  &  Navigation  Co.  Bridge  over  Willamette  River,  Portland,  Oregon. 


ART.  136  STABILITY   OF  PIERS  409 

From  the  bottom  to  the  top  the  sides  are  battered  i  inch  to 
the  foot. 

The  side  walls  are  18  inches  thick  and  *"are  ^reinforced  as 
vertical  slabs  spanning  horizontally  between  the  columns  and 
vertically  between  the  horizontal  diaphragms.  .  .  . 

"Between  the  outside  walls  of  the  hollow  superstructure  are 
seven  reinforced-concrete  horizontal  diaphragms  each  2  feet 
thick,  which  are  designed  as  flat  plates  that  may  be  loaded  from 
above  or  below.  ...  At  the  center  of  each  diaphragm  is  a 
3-foot  circular  hole  which  permits  the  free  passage  of  water 
between  the  eight  stories.  ...  In  one  side  of  the  lowest 
story  is  an  opening  12  inches  wide  and  the  full  height  of  that 
story  so  water  may  rise  and  fall  inside  the  pier  with  variations 
in  the  stage  of  the  river.  The  reinforced-concrete  walls,  .  .  . 
therefore,  are  not  normally  subject  to  a  head  of  water,  but  the 
design  provides  for  any  emergency  that  may  occur  by  including 
in  them  reinforcement  placed  so  that  a  head  may  be  brought 
against  the  walls  and  diaphragms  from  any  direction." 

ART.  136.     STABILITY  OF  PIERS 

LOADS. — The  vertical  forces  to  be  sustained  on  any  horizontal 
plane  of  a  bridge  pier  are  the  live  load,  impact  load,  weight  of 
superstructure,  and  weight  of  pier  above  the  plane  in  question. 
Impact  loads  are  usually  ignored,  but  more  generally  on  high- 
way than  on  railroad  bridge  piers.  For  the  latter  some  con- 
sideration should  be  given  to  impact  forces  for  low  piers  and 
for  the  upper  part  of  high  piers. 

The  lateral  forces  to  be  resisted  by  a  railroad  pier  are  tractive 
forces,  wind  on  train,  wind  on  trusses,  wind  on  pier,  river  cur- 
rent, and  ice  pressure.  It  is  customary  to  specify  a  tractive 
force  equal  to  0.2  of  the  live  load;  where  the  bridge  is  a  double- 
track  structure  some  authorities  specify  a  full  live  load  on 
both  tracks  and  others  on  one  track,  the  latter  being  more  gen- 
eral. For  highway  bridge  piers  tractive  forces  may  usually 
be  neglected. 

1  Engineering  Record,  vol.  62,  page  160,  Aug.  6,  1910. 


410  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

The  wind  load  on  train  and  trusses  should  be  the  same  as 
those  used  in  designing  the  superstructure,  which  is  customarily 
taken  at  30  pounds  per  square  foot  of  exposed  vertical  surface 
of  both  trusses  and  train,  or  150  pounds  per  linear  foot  of  bridge 
for  each  lateral  system,  applied  at  the  panel  points,  and  300 
pounds  per  linear  foot  of  train  applied  at  a  point  7  feet  above 
the  base  of  rail.  Wind  on  the  end  of  the  pier  may  be  taken  at 
30  pounds  per  square  foot  where  the  ends  are  without  starlings 
and  20  pounds  per  square  foot  of  vertical  projection  where 
starlings  are  present. 

The  law  governing  the  pressure  on  bridge  piers  due  to  a  river 
current  is  not  definitely  known.  The  formula  P=(Kwv2)/2g 
is  frequently  used,  in  which  P  is  the  pressure  in  pounds  per 
square  foot  of  vertical  projection,  K  a  constant,  v  the  velocity 
of  current  in  feet  per  second,  w  the  weight  of  a  cubic  foot  of 
water,  and  g  the  acceleration  due  to  gravity  (approximately 
32.2  feet  per  second  per  second).  GREINER  in  his  General 
Specifications  for  Bridges,  Part  III,  Substructures  and  Concrete 
Bridges,  gives  a  value  for  (Kw)/2g  of  1.5  for  flat  surfaces  and 
one-half  of  this  for  rounded  surfaces,  with  a  minimum  of  150 
pounds  per  square  foot  for  flat  surfaces  subjected  to  freshets  and 
50  pounds  in  tidal  streams,  with  one-half  of  these  values  for 
rounded  ends. 

Experiments  show  that  the  velocity  varies  with  the  depth 
approximately  as  the  ordinates  of  an  ellipse,  the  maximum  being 
somewhat  below  the  surface.  The  center  of  pressure  is  com- 
monly assumed  at  one-third  the  distance  from  the  water  surface 
to  the  river  bed.  This  assumption  is  on  the  safe  side. 

Ice  exerts  its  greatest  pressure  when  in  the  form  of  a  field  of 
moving  ice  forcing  its  way  past  the  pier.  In  this  condition  the 
ice  is  more  or  less  soft.  In  the  specifications  noted  above  a 
value  of  50  ooo  pounds  per  foot  of  pier  width  for  a  zo-inch  thick- 
ness of  ice  (417  pounds  per  square  inch)  is  given  for  flat  surfaces, 
and  one-half  of  this  value  for  rounded  surfaces.  Other  thick- 
nesses will  have  proportionate  values.  For  the  North  Side 
Point  Bridge,  Pittsburgh,  Pa.,  the  river  piers,  which  had  rounded 
ends,  were  designed  to  resist  a  horizontal  ice  pressure  of  48  ooo 


ART.  137  EXAMPLE   OF   PIER  DESIGN  411 

pounds  per  linear  foot  of  width.  A  value  used  in  the  design  of 
a  number  of  large  dams  in  this  country  is  47  ooo  pounds  per 
linear  foot  of  width. 

METHODS  OF  FAILURE  OF  BRIDGE  PIERS. — To  be  stable  a  pier 
must  be  safe  against  sliding  on  any  horizontal  section,  crushing 
at  the  toe  of  any  horizontal  section,  and  free  from  tension  at  the 
heel  of  any  horizontal  section;  this  also  applies  to  the  base  of 
the  pier.  For  a  rectangular  or  nearly  rectangular  sec- 
tion the  last  condition  will  obtain  if  the  resultant  of  all  the 
forces  above  the  plane  in  question  cuts  the  section  within  the 
middle  third. 

The  forces  resisting  sliding  are  friction  of  masonry  on  masonry 
for  stone  masonry  piers,  the  shearing  strength  of  the  concrete  for 
concrete  piers,  and  a  combination  of  both  for  combination  piers. 
For  a  table  giving  friction  values  for  various  kinds  of  stone 
masonry  and  for  the  shearing  strength  of  concrete  see  American 
Civil  Engineers'  Pocket  Book,  page  577.  If  the  pier  dimensions 
at  the  top  accord  with  standard  practice  as  outlined  in  Art. 
132,  and  if  the  pier  has  the  conventional  batter  of  i  in  12  or 
i  in  24,  all  sections  will  be  amply  safe  against  sliding. 

DOUGLAS  1  recommends  the  following  allowable  compressive 
unit-stresses  in  pounds  per  square  inch:  Stone  masonry  with 
1-2  portland  cement  mortar  and  joints  not  over  \  inch  thick, 
granite,  700;  hard  limestone,  650;  medium  limestone  and  mar- 
ble, 600;  soft  limestone  and  sandstone,  500;  where  joints  are 
over  \  inch  thick,  450  pounds  for  all  kinds  of  sound  building 
stones;  for  1-2-4  concrete,  450;  1-3-6  concrete,  350;  and 
1-4-8  concrete,  250. 

ART.  137.    EXAMPLE  OF  PIER  DESIGN 

The  following  example  which  analyzes  the  pressures  on  the 
foundation  of  Pier  5  (Fig.  1370)  of  the  Tennessee  River  bridge 
of  the  Illinois  Central  Railroad,  is  taken  for  the  most  part  from 
an  article  by  W.  M.  TORRANCE  in  Engineering  News,  vol.  53, 
page  548,  May  25,  1905.  Wind  on  pier,  current  and  ice  were 

'  See  American  Civil  Engineers'  Pocket  Book,  page  576. 


412  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

nol  considered  in  the  original  article.  The  bed  of  the  river  is 
slightly  exposed  at  low  water. 

11  Yardage  of  concrete: 
Upper  2  ft.  of  coping,  1-2-4  concrete;  area  in  plan,  609 

sq.  ft.;  volume 45  cu.  yds. 

Lower  2  ft.  of  coping,  1-25-6  concrete;  area  in  plan,  556 

sq.  ft. ;  volume 41  cu.  yds. 

Shaft  of  pier,  1-2^-6  concrete;  top  area,  490.5  sq.  ft.; 

bottom  area,  786.6  sq.  ft.;  medium  area,  631.1  sq.  ft.; 

volume  by  prismoidal  formula  (for  height  56.86  ft.) ....    i  335  cu.  yds. 
Footing  course,  1-3-6  concrete;  top  area,  926.5  sq.  ft.; 

bottom  area,  i  801.8  sq.  ft.;  medium  area,  i  321.9  sq. 

ft. ;  volume  by  prismoidal  formula  (for  height  of  6  ft) ...      298  cu.  yds. 
Foundation  course,  1-3-6  concrete;  volume,  4Xy2Xf  f .      352  cu.  yds. 
Summary: 

1-2-4  concrete  in  coping 45  cu.  yds. 

1-2^-6  concrete  in  coping  and  shaft. . .    i  376  cu.  yds. 
1-3-6  concrete  in  footing  and  founda- 
tion  '     650  cu.  yds. 

Total 2  071  cu.  yds. 

Weightof  pier,  at  155  Ibs.  per  cu.  ft.,  2  071X27X155. ...  8667000  Ibs. 
Dead  load,  three  trusses  with  ballast  floor,  9  126X300.  .  .  2  738  ooo  Ibs. 
Live  load  from  300  ft.  of  double-track  train  loads, 

5000  X 2X300 3000000  Ibs. 

Total  gravity  load  on  foundation 14  405  ooo  Ibs. 

"The  tractive  force  on  the  bridge  is  taken  at  two-tenths  of  the  live  load, 
as  already  stated;  for  each  pier  in  question,  that  is 

Tractive  force  =  3  000000X0.2  =  600  ooo  Ibs. 

"Considering  that  this  force  acts  in  line  of  the  lower  chord  pins  (the 
trusses  and  floor  system  take  care  of  it  down  to  that  level),1  there  results 
Maximum  tractive  moment  about  foundation  bed,  in  direction  of  tracks  is 

600000X72.35  =  43410000  ft. -Ibs. 

It  will  be  noticed  that  the  tractive  force  is  calculated  on  the  full  double- 
track  load,  which  provides  for  its  being  called  into  play  from  both  tracks 
in  the  same  direction  simultaneously." 

To  get  the  moments  transverse  to  the  bridge,  there  is  a  wind 
load  on  the  upper  lateral  system  of  300X150  =  45000  Ibs., 
wind  load  on  the" lower  system  of  the  same  amount,  and  wind 

1  An  assumption  on  the  safe  side  and  involving  an  error  less  than  2  percent 
in  this  case. 


ART.  137 


EXAMPLE   OF   PIER   DESIGN 


413 


load  on  train  of  300X300=90000  Ibs.  acting  at  a  point  7  feet 
above  the  base  of  rail.  Multiplying  each  of  these  forces  by  their 
respective  distances  from  the  base  of  footing  the  overturning 
moment  for  wind  on  trusses  is  8  100  ooo  ft. -Ibs.,  and  for  wind  on 


^  Base  of  Ran.  EI.IIO.O  for  Ballaitrct  Floor 

\    BasToTRairtliO^O^ 
with  Timber  Ties 


High  Water  El.  95.0 


Low  Water.  El.  46.0 


J  v>    I      El.31.0      \    I 


Side        Eieva-t-ion . 


looooooooo  oT<fc; 

OOOOOOOOOOO'O 

>ooooooooooo 

ooooooooooo  o 

ooboooooooo 


oooooooooooo 

)OOOOOOOOOOO 

oooooooooooo 

,|"-  .'"h  OOOOOOOOOOO 

\Base  Castinji'tO  ooooooooooo 


OOOOOOOG- 

•e-o 


33  'c?*~  --------  *1 

End    Elevation. 


FIG.  1370.  —  River  Pier  5, 
Illinois  Central  Railroad 
Bridge  over  Tennessee  River, 
Gilbertsville,  Ky. 

NOTE.  —  Top    of    coping   to 
base    of     rail    is    7    feet    5.375 
inches  instead  of   10  feet.     Ele- 
vation  of  base  of  rail  is  109.31 
instead  of   109.0  feet. 


Half    Top   Plan.    |  Half   Pile    Plan 


•ain  is  7  740  ooo  ft. -Ibs.,  making  a  total  of  15  840  ooo  ft.-lbs.  for 
ind  on  superstructure. 

The  projection,  on  a  vertical  plane  transverse  to  the  pier, 
)f  the  part  subject  to  wind  is  675  square  feet.     The  moment 


414  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

about  the  foundation  bed  due  to  wind  on  pier  =20X675X3  1.5 
is  425  200  ft.-lbs. 

The  moment  about  the  foundation  bed  due  to  river  current, 
assuming  a  maximum  velocity  of  10  feet  per  second,  is  0.75  X 
io2X6o2X22.5  =  i  01  6  ooo  ft.-lbs. 

The  moment  about  the  foundation  bed  due  to  the  pressure  of 
a  lo-inch  thickness  of  ice  at  50  ooo  Ibs.  per  foot  of  width  of  pier 
is  25000X10.35X53.6  =  13  869000  ft.-lbs. 

The  following  computations  of  unit  loads  at  base  are  made: 
First,  by  considering  the  earth  to  take  all  the  load;  and  second, 
considering  the  piles  to  take  all  the  load: 

Direct  load  on  base  due  to, 

Weight  of  Superstructure 
Per  sq.  ft  ..............  2  738  0007(72X33)=   1  152  Ibs.  =   0.58  tons. 

Per  pile  ...............  2  738  000/306          =  8  950  Ibs.  =  4.47  tons. 

Weight  of  Substructure 
Per  sq.  ft  ..............  8  667  0007(72X33)=   3  650  Ibs.  =   1.82  tons. 

Per  pile  ...............  8  667  000/306          =  28  330  Ibs.  =  14.17  tons. 

Live  Load 

Per  sq.  ft.  ............  3  ooo  0007(72X33)=   i  264  Ibs.  =  0.63  tons. 

Per  pile  ...............  3  ooo  000/306          =   9  800  Ibs.  =  4.90  tons. 

Reduction  of  pressure  due  to  uplift  at  high  water: 

Per  sq.  ft  ..............  3  260  000/^2X33)  =   i  372  Ibs.  =  0.69  tons. 

Per  pile  ...............  3  260  000/306          =  10  660  Ibs.  =  5.33  tons. 

Reduction  of  pressure  due  to  uplift  at  low  water: 

Per  sq.  ft  ..............  i  340  000/^2X33)  =      564  Ibs.  =  0.29  tons. 

Per  pile  ...............  i  340  000/306          =  4  380  Ibs.  =  2.19  tons. 

The  moment  of  inertia  of  the  base  in  bi-quadratic  feet  about  an  axis 
through  the  center  of  gravity  and  parallel  with  the  long  axis  of  the  pier  is 


The  maximum  and  minimum  pressures  on  the  base  due  to 
tractive  forces  are  (43410000X16.5)7215  600=  ±3  320  Ibs. 
per  sq.  ft.  =  =*=  1.66  tons  per  sq.  ft. 

The  moment  of  inertia  of  the  pile  tops  about  an  axis  through 
the  center  of  gravity  and  parallel  with  the  long  axis  of  the  pier, 
and  in  units  of  the  area  of  one  pile  top  times  quadratic  feet 
(neglecting  moment  of  inertia  about  the  gravity  axis  of  the  in- 


ART.  137  EXAMPLE    OF   PIER   DESIGN  415 


dividual  pile  tops)  is  2[24( 
=  26860. 

The  maximum  and  minimum  loads  per  pile  due  to  tractive 
force  are  (43410000X15)726860=  ±24  250  Ibs.  =  ="=12.12  tons. 

The  moment  of  inertia  of  the  base  in  bi-quadratic  feet  about 
an  axis  through  the  center^  of  gravity  and  parallel  with  the  short 
axis  of  the  pier  is  (33X723)/i2  =  i  026000. 

The  maximum  and  minimum  pressures  per  square  foot  on  the 
base  due  to  the  following: 
For  wind  on  trusses, 

(8  100000X36)71  02600=  ='=0284284  Ibs.  =  =*=o.  14  tons. 
For  wind  on  train, 

(7  740  000X36)71  026  000=  =*=  272  Ibs.  =  =•=  0.14  tons. 
For  wind  on  pier, 

(425  200X36)71  026000=  ===  14.9  Ibs.  =±0.007  tons. 
For  river  current  and  ice, 

(14  880  000X36)71  026  000=  ±522  Ibs.  =  ="=0.26  tons. 

The  moment  of  inertia  of  the  pile  tops  about  an  axis  through 
the  center  of  gravity  and  parallel  with  the  short  axis  of  the  pier, 
and  in  units  of  the  area  of  one  pile  top  times  quadratic  feet 
(neglecting  moment  of  inertia  about  the  gravity  axis  of  the  indi- 
vidual pile  tops)  is  2[7(^2+4^2+.  •  .34^52H6(32+62+.  .  . 


The  maximum  and  minimum  loads  per  pile  are  as  follows: 
For  wind  on  trusses, 

.     (8  100000X34.5)7127  100=  ±  2  200  Ibs.  ==fci.io  tons. 
For  wind  on  train, 

(7  740000X34.5)7127  100=  ="=  2  100  Ibs.  ==*=i.  05  tons. 
For  wind  on  pier, 

(425  200X34.5)7127  100=  ±115  Ibs.  =  ='=0.057  tons,  and 
For  river  current  and  ice, 

(14880000X34.5)7127  100=  ±4040^3  =  =1=2.o2  tons. 
It  will  be  seen  that  the  maximum  pressure,  assuming  no  up- 
lift, is  5.23  tons  per  square  foot  or  39.83  tons  per  pile,  while 
with  uplift  the  values  are  respectively  4.69  and  35.68.  The 
minimum  values  show  that  compression  always  exists,  although 
at  some  points  it  is  very  slight. 


416  ORDINARY  BRIDGE   PIERS  CHAP.  XII 

Summary  of  unit-loading  on  foundation: 

Tons  per  sq.  ft.  Tons  per  pile 

Weight  of  superstructure o.  58  4-47 

Weight  of  pier 1.82  14 . 17 

Live  load o .  63  4 . 90 

Uplift  at  high  water 0.69  5.33 

Uplift  at  low  water o.  29  2 . 19 

Tractive  force 1.66  12.12 

Wind  on  trusses : 0.14  i .  10 

Wind  on  train o.  14  i  .05 

Wind  on  pier o .  01  p .  06 

River  current  and  ice o .  26  2 . 02 

f  Max.. .  ^.23  39.83 

Assuming  no  uplift       \  .  _.  ^    6 

I  Mm 0.83  7.25 

.  ,  „      ,.,,       [Max 4.69  35-68 

Assuming  full  uplift     {  A ... 

\  Mm 0.14  1.92 

Regarding  the  effect  of  uplift,  in  a  case  like  this,  where  water 
is  more  or  less  free  to  get  under  the  pier  there  is  no  question 
of  its  action.  On  the  other  hand  it  cannot  act  with  full  hydro- 
static pressure  on  account  of  the  presence  of  gravel  and  of  the 
pile  tops  bearing  against  the  pier. 

A  few  words  of  explanation  regarding  the  method  of  getting 
the  maximum  and  minimum  values  in  the  above  table  may  be 
advisable.  In  this  pier,  where  the  top  is  but  a  slight  distance 
above  high  water,  wind  on  pier  cannot  act  simultaneously  with 
ice  and  current,  or  at  least,  that  which  acts  may  be  neglected. 
In  computing  the  minimum  pressure  the  live  load  is  included 
as  the  negative  values  due  to  tractive  force  and  wind  on  train 
overbalanced  the  positive  value  due  to  direct  pressure.  In 
finding  the  maximum  pressure  by  considering  uplift,  the  condi- 
tions obtaining  at  low  water  were  used,  since  these  give  a  greater 
value  than  for  high  water.  In  getting  the  minimum  values 
with  uplift,  high  water  was  used. 

In  studying  the  horizontal  section  of  the  pier  the  same  method 
is  to  be  followed  as  in  obtaining  the  pressure  on  the  base,  ex- 
cept that  uplift  will  be  omitted. 


CHAPTER  XIII 
CYLINDER  AND  PIVOT  PIERS 

ART.  138.     GENERAL  ARRANGEMENT 

For  light  bridges  the  massive  piers  and  foundations  described 
in  the  preceding  articles  may  furnish  strength  and  stability  far 
in  excess  of  the  requirements.  This  is  due  largely  to  the  fact 
that  the  dimensions  of  the  pier  are  governed  not  alone  by  the 
magnitude  of  the  loads  and  the  required  bearing  area  on  the 
foundations,  but  also  by  the  distance  between  superstructure 
pedestals  or  base  plates,  size  of  pedestals,  and  necessary  edge 
distances.  For  this  reason  in  many  cases  it  may  prove  econom- 


FIG.  1386. — Oxford  Mill  Pond  Bridge,  Chicago  &  Northwestern  Railway. 

ical  to  use  cylinder  piers.  This  type  of  pier  consists  of  a  number 
of  long  slender  cylinders  composed  in  most  cases  of  steel  shells 
filled  with  concrete.  When  used  to  support  fixed  spans  the  pier 
consists  of  two  or  more  cylinders  in  a  line  perpendicular,  or 
nearly  so,  to  the  direction  of  the  bridge,  as  illustrated  in  Fig. 
1380;  when  used  to  support  a  trestle  four  cylinders  are  used,  as 
illustrated  in  Fig.  1386;  while  for  a  pivot  pier  one  cylinder  at 
the  center  and  a  number  of  others  on  the  circumference  of  a 
circle  are  frequently  used.  Pivot  piers  are  also  formed  of  one 
large  cylinder;  this  type  is  described  in  Art.  142. 
27  417 


41 8  CYLINDER   AND   PIVOT   PIERS  CHAP.  XIII 

The  cylinders  may  be  composed  of  concrete,  brick,  or  stone 
masonry.  They  usually  have  a  metal  shell  of  cast  iron,  wrought 
iron,  or  steel.  Wrought  iron  is  not  used  at  the  present  time. 

Cylinders  piers  may  be  founded  on  bedrock  or  hard-pan,  on 
piles,  open  cylinder  caissons,  or  pneumatic  cylinder  caissons. 
When  founded  on  caissons  the  pier  is  simply  a  continuation  of 
the  caisson,  and  as  such  is  described  in  Arts.  85,  101  and  102. 
The  following  articles  deal  chiefly  with  the  cylinder  pier  founded 
on  bedrock  or  on  piles,  taking  up  only  those  features  of  the  other 
two  types  which  have  not  already  been  described. 

ART.  139.     METAL  SHELL  CYLINDER  PIERS 

ON  PILES. — Where  the  cylinders  are  of  small  diameter,  piles 
are  driven  and  the  cylinder  shells  set  over  the  same  and  filled 
with  concrete.  With  the  larger  cylinders  the  shells  are  often 
placed  before  driving  the  piles.  If  the  top  stratum  is  composed 
of  silt  or  other  soft  material  this  should  be  excavated  to  a  fairly 
solid  material  in  order  that  the  piles  may  have  lateral  support; 
care  should  also  be  taken  to  have  the  excavation  carried  below 
low- water  level  as  well  as  to  a  depth  free  from  any  danger  of 
scour.  After  excavating,  the  piles  are  driven  and  their  tops  cut 
off  at  some  elevation  above  the  surface  of  the  ground.  The  cyl- 
inder shells  rest  on  the  river  bottom  or  are  sunk  a  few  feet  into 
the  same.  If  clay  is  penetrated  it  is  sometimes  possible  to  pump 
out  the  water  and  place  the  concrete  filling  in  the  dry;  otherwise 
a  few  feet  of  concrete  are  placed  in  the  bottom,  and  allowed  to 
harden  a  few  days;  after  which  the  cylinder  is  pumped  out  and 
the  remainder  of  the  filling  placed  in  the  dry.  The  concrete 
placed  through  the  water  should  have  about  20  percent  more 
cement  in  it  than  that  placed  in  the  dry  to  allow  for  the  washing- 
out  action  of  the  water. 

The  cylinder  pier  with  pile  foundations  was  first  used  in  1868 
for  the  substructure  of  a  bridge  in  Rhode  Island  as  stated  in 
BAKER'S  Masonry  Construction. 

The  Tensas  River  bridge  in  Alabama,  built  in  1870,  was  one 
of  the  early  large  structures  using  this  type  of  foundation. 


ART.  139 


METAL    SHELL   CYLINDER   PIERS 


419 


The  shells,  of  cast  iron  i^  inches  thick,  had  exterior  diameters 
of  4  and  6  feet,  and  were  in  sections  10  feet  long,  the  sections 
being  united  by  bolts  through  interior  flanges  2  inches  thick  and 


riTTTi 

••MM/ 

FIG.  1390. — Cylinder  Piers  of  Victoria  Bridge  over  Bear  River,  Nova  Scotia. 

3  inches  wide.  For  the  fixed  spans  of  the  bridge  each  pier  was 
composed  of  two  6-foot  diameter  cylinders  16  feet  apart,  while 
the  pivot  pier  had  a  central  cylinder  6  feet  in  diameter  and  six 


42O 


CYLINDER  AND  PIVOT  PIERS 


CHAP.  XIII 


4-foot  cylinders  arranged  hexagonally  on  the  circumference  of  a 
circle  25  feet  in  diameter. 

Squared  piles  arranged  closely  together,  with  12  in  each  of  the 
6-foot  cylinders  and  5  in  the  4-foot  ones,  were  driven  to  a  depth 
of  not  less  than  20  feet  into  the  sandy  bed  of  the  river.  Their 
tops  were  then  tied  together  with  bolts  and  sawed  off  at  low- 
water  level,  15  feet  above  the  bed  of  the  river.  The  cylinders 
were  then  sunk  10  feet  into  the  bed  of  the  river  and  enveloping 
the  pile  clusters,  pumped  out  and  filled  with  concrete. 

The  shells  for  the 
piers  of  the  Victoria 
bridge  in  Nova  Scotia, 
constructed  in  1888, 
were  made  of  wrought 
iron.  The  rim  of  the 
shells  rested  on  piles 
cut  off  at  the  surface  of 
the  ground;  other  piles 
extended  up  into  the 
cylinder  as  shown  in 
Fig.  139  a.1  The  piers 
were  protected  against 
scour  and  braced  by 
cribs  filled  with  stone 
and  concrete,  as  well  as 
by  outside  rip-rap. 

Much  larger  cylinders  than  those  above  described  were  used 
in  the  Norfolk  and  Western  Railroad  bridge  No.  5  across  Eliza- 
beth River  at  Norfolk,  Va.  The  lower  part  of  the  cylinder  for 
Pier  2  consisted  of  a  f-inch  steel  shell  20  feet  in  diameter  and  15 
feet  9  inches  long,  stiffened  by  ^X^-inch  angles  spaced  5  feet 
apart  vertically.  A  temporary  upper  section  of  the  same  diam- 
eter and  high  enough  to  reach  to  above  water-level  was  attached 
to  act  as  a  cofferdam.  The  shell  was  then  let  down  through  the 
water,  23  feet  deep  at  low  tide,  and  sunk  about  18  feet  into  the 

1  Bridge  Foundations  in  Nova  Scotia,  by  MARTIN  MURPHY,  Trans.  Am.  Soc. 
C.  E.,  vol.  29,  page  629,  Sept.,  1893. 


Rail  Grillage,  S  Layers 
ecrch  of  6, 85  Ib.  Rails 


p ; 


FIG.   1396. — Typical  Cylinder  Pier. 
River  Bridge,  N.  &  W.  R.R. 


Elizabeth 


ART.  139  METAL   SHELL   CYLINDER   PIERS  421 

mud  by  dropping  it  a  few  times  from  a  considerable  height. 
The  material  was  then  excavated  to  the  bottom  edge  of  the  shell 
after  which  80  piles  were  driven,  and  cut  off  by  a  diver  at  an 
elevation  7  feet  above  the  cylinder  bottom.  Concrete  of  a  1-2-4 
mixture  was  then  deposited  through  the  water  to  within  6 
inches  of  the  tops  of  the  piles.  After  allowing  this  to  set  4  or 
5  days  the  cylinder  was  pumped  out  and  a  2-foot  layer  of  con- 
crete, enclosing  a  grillage  of  rails,  was  placed  over  the  tops  of  the 
piles  to  more  uniformly  distribute  the  load  over  them. 

As  shown  in  Fig.  1396  a  cast-iron  cylinder  10  feet  in  diameter 
was  then  placed  in  the  larger  cylinder.  This  shell  was  made  in 
four  lengths  of  8  feet  9  inches  each  and  each  length  was  composed 
of  four  segments,  the  whole  being  bolted  together  through  inside 
flanges.  The  metal  was  i  inch  thick.  In  the  diagram  the  upper 
horizontal  line  represents  the  base  of  rail. 

Round  iron  bars  i|  inches  in  diameter  and  i\  feet  long  were 
run  through  the  cast-iron  shell  near  the  bottom,  and  the  outside 
cylinder  was  then  filled  with  1-2-4  concrete,  which  was  crowned 
up  on  a  3o-degree  slope.  Concrete  was  placed  in  the  ro-foot 
cylinder  to  within  2  feet  of  the  top  and  a  heavy  beam  grillage  was 
set  on  this,  crowned,  and  grouted  with  concrete.  The  outside 
cofferdam  was  then  removed.  Cast  iron  was  used  for  the  upper 
part  of  the  pier  because  of  its  better  lasting  qualities  when  only 
periodically  immersed. 

In  the  foregoing  examples,  in  all  cases  some  of  the  piles 
were  extended  well  up  into  the  cylinder.  The  advantage  of  this 
is  the  added  stability  against  sliding  and  overturning.  If  the 
cylinders  are  not  subjected  to  horizontal  forces  of  any  consider- 
able magnitude  the  piling  may  be  cut  at  the  base  of  the  cylin- 
der or  lower.  If  this  is  done  the  piles  are  surmounted  with 
a  concrete  capping  or  timber  grillage  and  the  cylinders 
placed  on  it. 

The  piers  for  the  approach  spans  of  the  Cairo  bridge  of  the 
Illinois  Central  Railroad  were  each  formed  of  two  8-foot  cyl- 
inders. Since  no  water  covered  the  site,  a  circular  pit  8  feet 
deep  was  dug  for  each  cylinder  and  12  oak  piles  driven  in  it. 
The  pits  were  then  filled  with  concrete  to  the  proper  elevation, 


422 


CYLINDER   AND   PIVOT   PIERS 


CHAP.  XIII 


FIG.   I3QC. — Cylinder  Piers  of  Avon   River   Bridge,   Windsor,    Nova  Scotia 


ART.  140 


DESIGN   AND    CONSTRUCTION 


423 


after  which  the  cylinders  were  placed  and  concrete  filled  in 
around  them  to  a  depth  of  6  inches.  The  cylinders  were  then 
filled  with  concrete. 

ON  ROCK  OR  HARD-PAN. — Where  the  bottom  is  rock  or  hard- 
pan  it  is  only  necessary  to  clean  and  level  off  the  site,  place  the 
cylinder,  and  fill  it  with  concrete.  Where  horizontal  forces 
occur  the  piers  must  be  fastened  to  the  foundation  bed  in  some 
manner.  This  may  be  done  by  drilling  holes  in  the  latter  and 
grouting  rails  or  steel  bars  into  the  same,  as  was  done  for  the 
piers  of  the  Avon  River  bridge,  Nova  Scotia,  illustrated  in 
Fig.  i$gc. 

ART.  140.     DESIGN  AND  CONSTRUCTION 

The  size  of  the  cylinder  will  depend  on  the  load  to  be  sup- 
ported and  the  character  of  the  foundation.  The  area  of  the 
base,  with  the  pile  founda- 
tion, is  governed  by  the 
number  of  piles  and  their 
spacing,  while  if  the  pier 
rests  on  rock  or  hard-pan 
the  area  is  governed  by  the 
allowable  bearing  pressure 
on  the  same.  The  area  of 
the  upper  part  of  the  pier 
will  depend  upon  the  size  of 
the  pedestals  or  base  plates 
of  the  bridge.  In  general  it 
is  advantageous  to  have  the 
diameter  of  the  cylinder  as 
small  as  possible,  to  avoid  re- 
stricting the  water  way  and 
offering  resistance  to  the 
current,  ice,  and  drift  ma- 
terial. Where  much  ice  and  drift  are  present  it  may  be  ad- 
visable to  use  a  pointed  nose,  as  illustrated  in  Fig.  1400. 

Where  the  required  diameters  at  the  top  and  bottom  differ 
materially,  a  shell  having  a  smaller  diameter  at  the  top  than  at 


Sectional    Plan 


L,4x4-. 


Plate    \    \   V Plate 


* 


Elevation 


Flatten  all 
rivets  on  out- 
side fo^ 


FIG.   1400;. — Cylinder  Pier  with  Pointed 
End. 


424  CYLINDER  AND  PIVOT  PIERS  CHAP.  XIII 

the  bottom  should  be  used.  This  may  be  done  by  using  two 
separate  shells  as  indicated  in  Fig.  1396  or  by  a  connection 
similar  to  Fig.  1400,  or  by  using  a  shell  in  the  form  of  a  frustum 
of  a  cone,  as  illustrated  in  Fig.  ioia. 

The  thickness  of  the  shell  is  usually  made  just  sufficient  to 
take  care  of  the  stresses  developed  in  handling  and  placing. 
Experience  has  demonstrated  that  it  is  inadvisable  to  use  less 
then  a  f-inch  thickness,  although  a  yV-inch  thickness  is  often 
specified  for  highway  bridge  cylinders.  A  thickness  of  more 
than  |  inch  will  seldom  be  required  even  for  large  cylinders. 
Complete  specifications  and  tables  giving  diameters  and  thick- 
ness of  shells  for  highway  bridge  piers  are  given  in  COOPER'S 
General  Specifications  for  Foundations  and  Substructures 
of  Highway  and  Electric  Railway  bridges. 

STABILITY  OF  PIERS. — The  four  possible  methods  of  failure 
are  undermining;  settling,  due  to  excessive  pressure  on  the 
foundation;  sliding;  and  overturning.  Undermining  is  placed 
first  because  of  the  many  failures  of  highway  bridge  piers  in 
this  country  due  to  this  cause.  Where  founded  on  caissons 
there  is  no  danger  from  this  source,  but  where  founded  on 
piles  care  should  be  taken  to  have  the  whole  length  of  the  piles 
well  below  any  possible  scouring  action,  otherwise  the  founda- 
tion may  collapse  through  lack  of  lateral  stability.  If  it  is 
impracticable  to  get  the  piles  down  to  such  an  elevation  cribs 
should  be  built  around  the  tops  as  shown  in  Fig.  1390.  The 
same  protection  should  be  given  the  foundation,  where  the 
material  composing  it  is  clay  or  hard-pan  or  even  the  softer 
kinds  of  rock,  if  the  piers  are  located  in  a  scouring  current. 

To  prevent  settlement  the  foundation,  if  composed  of  piles, 
should  be  designed  in  accordance  with  the  rules  given  in 
Chapter  III  with  regard  to  safe  loads  on  piles;  or  if  hard-pan 
or  rock,  in  accordance  with  safe  unit-loads  as  given  in  Art. 
179.  The  vertical  load  may  usually  be  assumed  as  uniformly 
distributed  over  the  base  of  the  cylinder,  for  the  transverse 
loads  are  resisted  by  a  truss-like  action  of  the  cylinders  and 
bracing.  Thus,  with  a  two-cylinder  pier,  in  addition  to  the 
vertical  loads  due  to  the  live  load,  weight  of  superstructure 


ART.  140 


DESIGN  AND   CONSTRUCTION 


425 


and  pier,  there  will  be  a  downward  vertical  load  on  one  cylin- 
der equal  to  the  moment  of  the  transverse  loads  about  the 
bottom  of  the  pier  divided  by  the  distance  between  cylinders 
center  to  center. 


Base  of  Rail 


Sectional         Side        Elevation 
Ground  Line 


Section 

on    Center  Line 

of   Pier 


ENG.  NEWS 


Plan 
FIG.   1406. — Cylinder  Piers  Braced  by  a  Truss  Encased  in  Reinforced  Concrete 

Where  forces  exist  tending  to  slide  the  pier,  if  a  pile  founda- 
tion is  used  some  of  the  piles  should  extend  well  up  into  the 
cylinder;  while  if  the  cylinders  rest  on  bedrock  they  should 
be  anchored  to  the  rock  surface.  A  rockfilled  crib  placed 


426  CYLINDER   AND   PIVOT   PIERS  CHAP.  XIII 

around  the  cylinders,  as  illustrated  in  Figs.  139^  and  c  will  add 
resistance  to  sliding. 

To  resist  overturning,  strong  and  rigid  bracing  should  con- 
nect the  cylinders.  Many  forms  of  bracing  are  illustrated  in 
the  accompanying  figures;  these  include  simple  ties  and  struts 
ofmetal  and  wood,  as  in  Figs.  1390  and  c\  latticed  girders,  as 
in  Fig.  1380;  plate  girders,  as  in  Fig.  ioi&;  double  plate  girders 
filled  with  concrete,  as  in  Fig.  101  a\  and  deep  trusses  embedded 
in  concrete,  Fig.  1406. 

ART.  141.  REINFORCED- CONCRETE  CYLINDER  PIERS 

One  of  the  disadvantages  of  the  metal- shell  type  of  pier  is  the 
necessity  of  keeping  it  painted.  Although  with  steel  shells  it 
is  not  customary  to  design  the  shell  to  take  any  of  the  load 
yet  it  is  advisable  to  prevent  the  same  from  rusting  for  two 
reasons:  First,  the  shell  takes  any  tensile  stresses  that  may 
develop  in  the  pier  due  to  eccentric  loading,  ice  pressure,  etc. ; 
and  second,  the  appearance  of  the  pier  during  the  rusting  of 
the  shell,  as  well  as  the  stained  appearance  of  the  concrete 
afterward  is  unsightly. 

The  metal  shell  may  be  avoided  by  building  the  pier  in  forms 
in  a  cofferdam  or  by  using  a  pre-molded  shell  of  reinforced 
concrete.  In  either  case  the  pier  should  be  well  reinforced 
with  steel  rods. 

Each  pier  of  a  bridge  at  Buffalo,  N.  Y.,  on  the  Lake  Shore  & 
Michigan  Southern  Railroad  was  formed  of  two  shafts,  30  feet 
6  inches  apart  on  centers,  braced  together  with  a  steel  girder 
encased  in  reinforced  concrete.  This  girder  served  to  transfer 
the  load  from  the  superstructure  to  the  shafts.  Each  shaft,  13 
feet  6  inches  in  diameter  and  about  51  feet  high,  rested  on  solid 
rock  36  feet  below  water-level.  The  shafts  were  constructed  in 
cofferdams  18  feet  in  diameter,  made  of  Lackawanna  steel 
sheet-piling  in  45-foot  lengths.  To  within  21  feet  of  the  top 
each  shaft  of  the  pier  was  octagonal  in  section  and  above  this 
circular.  The  reinforcement  consisted  of  80  vertical  ij-inch 
corrugated  bars  extending  from  the  top  to  a  point  30  feet 


ART.  141 


REINFORCED-CONCRETE    CYLINDER   PIERS 


427 


below  and  lying  on  the  circumference  of  a  circle  6  inches  inside 
of  the  surface. 

The  strut,  composed  of  a  reinforced-concrete  girder  4  feet 
6  inches  deep  and  about  5  feet  wide,  was  reinforced  with  48 
corrugated  bars  ij  inches  square  and  30  feet  long,  spaced  about 
6  inches  center  to  center  all  around  the  strut,  6  inches  from  side 


Top_Qf_Roadwgy_ 


Pier  6  Section  A-A 

FIG.  i4ia. — Reinforced-concrete  Double-cylinder  Pier. 

and  bottom  faces  and  12  inches  below  the  top  face.     As  stated 
above  it  was  further  reinforced  with  a  steel  plate  girder. 

Fig.  14 1  a  illustrates  the  reinforced-concrete  cylinder  piers  of  a 
highway  bridge  over  the  St.  Croix  River  at  Hudson,  Wis. 
Each  pier  consists  of  two  reinforced-concrete  shafts  from  4  to 
5  feet  in  diameter  and  braced  together  with  reinforced-concrete 


428 


CYLINDER   AND   PIVOT   PIERS 


CHAP.  XIII 


The 


webs.     These    shafts    had    separate    pile    foundations, 
shafts  were  cast  in  wooden  forms  in  i4-foot  sections. 

In  constructing  the  piers  for  a  bridge  across  the  River  Wan- 
beck,  Stakeford,  England,  the  cylinders  were  formed  of  sections 
of  reinforced-concrete  shells  48  inches  in  diameter  placed  over 
i4-inch  pre-molded  concrete  piles  driven  into  the  river.  The 


FIG.   1416. — Braced  Bent  of  Reinforced-concrete  Cylinder  Piers. 

cylinders  rested  on  the  river  bottom.  After  placing  the  shells, 
reinforcing  rods  were  lowered  into  the  same  and  the  cylinders 
filled  with  concrete.  The  bracing  was  also  of  reinforced  con- 
crete. The  structure  is  illustrated  in  Fig.  14 ib. 

ART.  142.     LARGE  CYLINDER  OR  PIVOT  PIERS 

This  type  of  pier,  used  almost  exclusively  for  the  center 
support  of  swing  spans,  resembles  the  cylinder  pier  in  shape  and 
the  ordinary  masonry  pier  in  massiveness.  The  same  types  of 
foundations,  kinds  of  material,  and  methods  of  construction  are 
used  as  for  ordinary  piers.  Where  protection  against  ice  and 
drift  is  necessary  it  is  furnished  by  means  of  an  independent  pier, 
often  constructed  of  long  piles. 


ART.  142 


LARGE    CYLINDER    OR   PIVOT   PIERS 


429 


Fig.  1420  illustrates  the  all-concrete  solid  pivot  pier  on  piles 
used  for  the  St.  Louis  River  bridge  near  New  Duluth,  Minn. 
The  depth  of  water  being  about  28  feet,  the  pier  was  constructed 
in  wooden  forms  inside  of  a  circular  steel  sheet-pile  cofferdam 
36  feet  in  diameter.  After  driving  the  piles  and  cutting  them 
off  about  4  feet  above  the  dredged  bottom,  a  6-foot  layer  of 
concrete  was  placed  to  form  the  36-foot 
diameter  footing  course,  the  sheet- 
piling  serving  as  a  form  for 
the  sides.  Above  this  footing 
course  the  form  for  the  pier  & 
consisted  of  a  wooden-stave  I 


run  n  rr 

\m 

u  u  u  li  y  iJ  UTli  u  u  u  lj  u 


Section  A-A 


Elevation  of  Center  Pier 


FIG.   1420. — Concrete  Pivot  Pier,  St.  Louis  River  Bridge,  Duluth,  Minn. 

water  tank  16  feet  high  having  a  side  batter  of  i  inch  to  the 
Foot  (Fig.  142  b).  The  second  lift  was  made  by  raising  the  tank 
and  planing  a  few  of  the  staves  to  fit  the  new  dimensions.  For 
the  coping  course  galvanized  iron  of  the  section  shown  in  the 
illustration  was  used.  A  grillage  of  24-inch  I-beams  distributed 
:he  load  over  the  pier. 
The  pivot  pier  construction  of  the  Dumbarton  bridge  of  the 


43° 


CYLINDER   AND   PIVOT   PIERS 


CHAP.  XIII 


Central  California  Railroad,  merits  particular  attention  because 
of  .its  simple  solution  of  a  difficult  problem.  At  the  site  the 
depth  of  water  at  low  tide  was  51  feet  and  at  high  tide  58  feet, 
with  a  maximum  velocity  of  current  of  4^  miles  an  hour.  The 
bottom  consisted  of  soft  mud  overlying  stiffer  material.  On 
account  of  the  great  depth  of  water  and  velocity  of  current  the 


--3F-"-- 


Use  these  hoops  for      { 
upper  forms  at  same  elevat'ipn. 


•Staves  2'x6*xl6'O* 
S  I.  S  and  beveled  to 


t.i 


^ 32'0" •- * 

Forms  for  Concrete  Center  Pier 

FIG.   1426. — Form   for    Constructing   Concrete   Pivot   Pier. 

cofferdam  process  was  not  practicable  and  caisson  foundations 
would  have  been  expensive.  Hence  it  was  decided  to  employ  a 
metal  shell  with  a  pile  foundation.  The  cylinder  had  a  diameter 
of  40  feet  and  was  72  feet  5  inches  high  in  five  vertical  sections, 
After  dredging  out  about  10  feet  of  the  soft  material  on  the 
bottom  the  first  section  of  the  cylinder  was  lowered.  This  was 
effected  by  first  lowering  a  guide  frame  of  structural  shapes  and 


ART.  142 


LARGE   CYLINDER   OR  PIVOT  PIERS 


431 


driving  its  feet  into  the  bottom,  after  which  the  section  of  the 
cylinder  was  placed  around  this  frame  and  lowered.  Inside  this 
section  141  piles  were  driven  to  a  penetration  of  about  30  feet 


Part     Side 
Elevation. 


Base  of  Rail,  El. 


I         <  n'n" s       High  Water  £1.95.0 

'  ~'~~ 


K 59  0 

Half   Elevation.     Half    Section. 


Half  Top   Plan.     Half   Pile  Plan 


FIG.  142^. — Reinforced-Concrete  Pivot  Pier,  Illinois  Central  Railroad  Bridge, 
Gilbertsville,  Ky. 

and  cut  off  below  low- water  level;  some  only  about  3  feet  below 
low  water  and  others  near  the  bottom.  On  completion  of  the 
pile  driving  more  sections  of  the  shell  were  added,  each  section 


432  CYLINDER   AND   PIVOT   PIERS  CHAP.  XIII 

being  filled  with  concrete  placed  through  the  water  to  within 
7  feet  of  the  top  before  another  section  was  added.  This  was 
the  highest  level  at  which  the  top  of  the  concrete  would  not  be 
disturbed  by  the  tidal  current  passing  over  the  top.  Further 
details  of  this  interesting  work  may  be  found  in  an  article  by 
E.  J.  SCHNEIDER  in  Transactions  of  the  American  Society  of 
Civil  Engineers,  vol.  76,  page  1572,  Dec.,  1913,  entitled  Con- 
struction Problems,  Dumbarton  bridge,  Central  California 
Railway;  or  in  Engineering  Record,  vol.  62,  page  172, 
Aug.  13,  1910. 

Where  the  lateral  forces  on  the  piers  are  small  it  is  not 
necessary  to  extend  the  piles  into  the  cylinders.  In  the  con- 
struction of  a  pivot  pier  in  the  Willamette  River,  Portland, 
Ore.,  where  the  depth  of  water  was  60  feet,  piles  were  driven 
and  cut  off  near  the  bottom.  A  timber  grillage  extending  to 
within  3  feet  of  low-water  mark  was  placed  on  the  piles. 
On  this  grillage  was  placed  a  steel  shell  46  feet  in  diameter 
about  30  feet  high,  which  was  filled  with  concrete  to  form 
the  pivot  pier. 

Fig.  83^  shows  the  pivot  pier  of  the  Chelsea  Bridge  North, 
Boston,  which  was  faced  with  stone  masonry.  The  foundation 
for  this  pier  is  described  in  Art.  83. 

As  in  the  case  of  ordinary  bridge  piers  the  tendency  at  present 
is  to  make  the  pivot  pier  of  hollow  construction,  leaving  out 
masonry  from  that  part  of  the  pier  that  is  but  slightly  stressed. 

Fig.  14  2C  shows  the  reinforced  concrete  hollow  pivot  pier  of 
the  Tenriessee  River  bridge  of  the  Illinois  Central  Railroad. 
The  hollow  space  is  domed  at  the  top  and  bottom.  The  entire 
load  from  the  superstructure  comes  on  the  pier  through  a  cast- 
iron  track  38  feet  in  diameter.  The  circular  center  line  of  the 
8-foot  wall  has  the  same  diameter,  thus  avoiding  eccentric 
stresses  in  the  pier. 


CHAPTER  XIV 


BRIDGE  ABUTMENTS 

ART.  143.     FORM  AND  DIMENSIONS 

A  bridge  abutment  is  a  masonry  structure  at  one  end  of  a 
bridge  used  for  the  double  purpose  of  transferring  the  loads 
from  the  bridge  superstructure  to  the  foundation  and  to  give 
such  lateral  support  to  the  adjacent  embankment  as  is  required 
to  maintain  it  in  position. 

The  abutment  serves  both  as  a  pier  and  as  a  retaining  wall. 
Because  of  the  latter  function,  involving  as  it  does  the  question 
of  earth  pressure,  any  possible  mathe- 
matical treatment  on  the  design  of 
abutments  has  not  yet  been  developed 
in  a  satisfactory  manner. 

Fig.  1436!  shows  a  typical  section 
of  an  abutment  through  its  center 
and  parallel  with  the  directon  of  the 
bridge.  A  is  the  bridge  seat,  which 
consists  of  a  horizontal  surface  on 
which  rest  the  end  bearings  of  the 
superstructure;  B  is  the  back  or 
parapet  wall,  which  supports  the 
upper  part  of  the  embankment  and 
prevents  the  same  from  spilling  down 
on  the  bridge  seat;  C  is  the  main  body 
or  stem  of  the  abutment;  and  D  is  the  footing. 

The  forces  acting  upon  the  abutment  are  as  shown  in  the  illus- 
tration: First,  the  loads  on  the  bridge  seat,  which  consist  of  a 
vertical  force  from  the  live  and  dead  loads  from  the  superstruc- 
ture and  a  horizontal  force  due  to  traction  and  in  some  cases  to 
expansion  and  contraction  of  the  bridge  spans;  second,  the 
28  433 


FIG.  1430. — Section  of  Abut- 
ment Indicating  the  External 
Forces  Acting  upon  It. 


434  BRIDGE   ABUTMENTS  CHAP.  XIV 

earth  pressure  from  the  embankment  against  the  back  of  the 
wall,  due  both  to  the  weight  of  embankment  and  weight  of  live 
load;  third,  the  weight  of  the  abutment;  and  fourth,  the  reac- 
tions from  the  foundation. 

Abutments  are  classified  according  to  their  form.  The  three 
original  types  are  the  wing-wall  abutment,  the  U-abutment, 
and  the  T-abutment.  At  present  there  are  many  modifications 
of  these  fundamental  types.  In  the  wing-wall  abutment  the 
wings,  which  may  be  parallel  with  the  face  of  the  wall  or  at  any 
angle  with  the  same,  serve  merely  to  keep*  the  embankment 
material  from  slipping  into  the  stream  or  moving  out  into  the 
roadway,  as  shown  in  Figs.  145^  and  b.  In  the  U-abutment  the 
wings  are  made  parallel  with  the  roadway.  The  front  wall  is 
usually  located  at  a  point  such  that  the  side  embankment  mate- 
rial, having  a  slope  of  ij  on  i  or  i  on  i,  will  not  extend  out 
beyond  the  face  of  the  abutment  (Fig.  1436).  The  T-abutment 
has  the  same  form  of  bridge  seat  as  the  wing-wall  and  U-abut- 
ment, but  instead  of  wings  it  has  a  solid  stem  which  supports 
the  track  or  roadway  back  to  a  point  at  which  the  embank- 
ment is  sufficiently  high  to  support  it.  This  type  is  illustrated 
in  Figs.  1467  and  g. 

DIMENSIONS  OF  ABUTMENTS. — Like  the  bridge  pier  the  dimen- 
sions of  the  bridge  abutment  will  vary  with  many  conditions, 
such  as  class  of  superstructure,  height  of  abutment,  type  of 
foundation,  and  kind  of  embankment.  However,  owing  to  the 
uncertainties  involved  in  the  design,  certain  dimensions  are 
being  standardized  to  a  large  extent. 

The  dimensions  of  the  top  of  an  abutment  will  depend  on  the 
same  factors  as  the  top  of  a  bridge  pier,  except  that  where  in  the 
latter  case  bearing  must  be  furnished  for  two  trusses  or  girders, 
in  the  former  case  there  must  be  a  width  sufficient  for  one  truss 
or  girder  bearing  plus  a  distance  e  (Fig.  1430)  which  is  neces- 
sary to  furnish  the  required  stability  to  the  parapet  wall.  The 
value  of  e  is  usually  taken  as  0.40^  or  0.45^  unless  the  parapet 
wall  is  reinforced. 

luThe  width  of  bridge  seats,  exclusive  of  the  projection  of 

1  General  Specifications  for  Bridges,  Part  III,  by  J.  E.  GREINER. 


ART.  143 


FORM  AND  DIMENSIONS 


435 


the  coping,  shall  be  at  least  12  inches  greater  than  required  for 
the  bed  plates  of  steel  superstructures,  and  the  length  of  bridge 
seats  shall  not  be  less  than  the  total  width  of  bridge  out  to 
out  of  bearings  plus  4  feet.  The  upper  surfaces  of  the  back 
and  slope  walls  shall  not  have  a  less  width  than  2  feet  for  rail- 
way and  if  feet  for  other  bridges.  The  thickness  of  coping 
shall  not  be  less  than  18  inches  for  railway,  and  12  inches  for 
other  bridges." 

Table  143  a  gives  the  approximate  minimum  dimensions  of 
thickness  and  length  under  coping  for  electric  railway  bridges. 

TABLE  No. 


Span 

Thickness  of  abutment  under  coping 
given 

=  thickness  of  back  wall  +  figures 
below 

Class  A 

Class  B                              Class  C 

S.  T. 

D.  T. 

S.  T. 

D.  T.             S.  T.            D.  T. 

25                  2-  o 

2-    2 

2-    O 

2-0                 2-0              2-0 

50                       2-    2 

2-  9 

2-    0 

2-2                 2-0              2-    O 

75                  2-  6 

3-  3 

2-    O 

2-6                 2-    O 

2-    0 

100                       2-    8 

3-  6 

2-    O 

2-8                 2-    O 

2-    2 

125                       2-10 

3-  9 

2-    2 

2-IO                 2-    O 

2-  4 

150                3-  o 

4-  o 

2-  4 

3-0                 2-0 

2-  6 

175                       3~    2 

4-  3 

2-  6 

3-2                 2-0 

2-    8 

200                3-  4 

4-  6 

2-  8 

3-4                 2-2 

2-IO 

250                3-  8 
300                4-  o 

5-    0                    2-1  I 

5-6              3-1 

3-8            2-5 
4-0            2-7 

3-  2 
3-6 

350                4-  4 
400               4-  8 

5-10 
6-  2 

3~  3 
3-  5 

4-4             2-9 

4-  8            2-1  i 

3-10 
4-  o 

Span 

Length  of  abutment  under  coping  =  distance  center  to  center  of 
trusses  +  figures  below 

Class  A 

Class  B 

Class  C 

S.  T. 

D.  T. 

S.  T. 

D.  T. 

S.  T. 

D.  T. 

SO 

3-6 

4-0 

3-6 

3-6 

3-6 

3-6 

IOO 

4-0 

5-o 

3-6 

4-0 

3-6 

3-6 

150 

4-6 

5-6 

4-0 

4-6 

3-6 

4-0 

2OO 

S-o 

6-0 

4-0 

5-o 

3-6 

4-6 

250 

S-o 

6-6 

4-6 

5-o 

4-0 

4-6 

300 

5-6 

7-0 

4-6 

5-6 

4-0 

5-o 

350 

6-0 

7-6 

4-6 

6-0 

4-6 

S-o 

4OO 

6-0 

7-6 

5-o 

6-0 

4-6 

5-6 

Note:  All  dimensions  are  expressed  in  feet  and  inches.  S.  T.  =  single  track; 
D.  T.  =  double  track.  Class  A,  heavy  traffic;  Class  B,  medium  traffic;  Class  C, 
light  traffic. 

lFrom  article  by  C.  C.  SCHNEIDER  in  Street  Railway  Journal,  Sept.  15,  1906. 


43  6  BRIDGE   ABUTMENTS  CHAP.  XIV 

The  thickness  of  the  stem  may  be  designed  in  accordance 
with  the  methods  outlined  in  Art.  144.  However,  owing  to 
the  uncertainties  involved  in  estimating  the  earth  pressure,  as 
well  as  to  the  possible  large  forces  resulting  from  the  freezing  of 
water  in  the  embankment,  the  thickness  at  any  point  should  not 
be  made  less  than  0.4  the  height  at  that  point.  Some  experi- 
enced engineers  specify  a  coefficient  of  0.5  where  the  abutment 
rests  directly  on  soil.  GREINER  states  that  J"the  thickness 
of  the  stem  or  back  wall  at  any  elevation  shall  not  be  less  than 
0.45  of  the  height  of  the  masonry  above  that  elevation  for  steam 
railway  bridges,  and  0.4  for  other  bridges." 

ART.  144.     DESIGN  AND  CONSTRUCTION 

Abutments  may  be  built  of  stone  masonry,  concrete,  or  rein- 
forced concrete.  For  the  reasons  given  in  Art.  133  stone 
masonry  is  but  little  used  at  present.  A  facing  of  stone  is  some- 
times used,  but  not  to  the  extent  that  it  is  used  for  piers,  since 
abutments  are  usually  not  subjected  to  the  action  of  the  current, 
with  its  accompanying  ice  and  drift  material.  Where  built 
of  concrete  it  is  advisable  to  use  a  small  amount  of  surface 
reinforcement  for  the  same  reasons  as  those  given  for  piers  in 
Art.  133.  According  to  GREINER,  "The  surface  bonding  rein- 
forcement shall  be  the  same  as  provided  for  piers,  but  no  hori- 
zontal layers  of  network  will  be  required." 

Solid  massive  abutments  may  be  made  with  1-2^-5  to  1-3-6 
concrete  below  the  coping,  with  a  1-2-4  mixture  for  copings 
and  parts  above  the  same.  For  reinforced-concrete  abutments 
all  concrete  should  be  a  1-2-4  mixture;  or  better,  one  part 
of  cement  to  six  parts  of  aggregate  (before  combining  the  sand 
and  stone),  the  sand  and  stone  being  in  such  proportions  as  will 
give  the  densest  concrete  as  determined  by  trial  mixtures. 

DESIGN  OF  ABUTMENTS. — The  vertical  loads  to  be  sustained 
on  any  horizontal  plane  are  the  live  load,  impact  load,  weight  of 
superstructure  and  weight  of  abutment  above  the  plane  in 
question.  Impact  may  usually  be  neglected. 

1  General  Specifications  for  Bridges,  Part  III,  by  J.  E.  GREINER. 


ART.  144  DESIGN  AND  CONSTRUCTION  437 

The  lateral  forces  parallel  to  the  axis  of  the  bridge  are  the 
tractive  force  and  the  pressure  from  the  embankment  due  to 
both  the  weight  of  the  embankment  material  and  the  live  load. 
At  right  angles  to  the  axis  of  the  bridge  are  the  wind  loads  from 
the  superstructure  and  on  the  abutment.  The  latter  two  are 
usually  neglected,  their  effect  being  slight  compared  with  the 
other  forces. 

Of  all  the  forces  coming  on  the  abutment  the  earth  pressure 
from  the  embankment  is  the  most  uncertain  in  its  effect  and 
the  most  difficult  to  analyze.  For  descriptions  of  various 
methods  of  computing  earth  pressure,  the  reader  is  referred  to 
HOWE'S  Retaining  Walls  for  Earth;  CHURCH'S  Mechanics  of 
Engineering;  and  TURNEAURE  and  MAURER'S  Principles  of 
Reinforced-Concrete  Construction.  The  other  forces,  with  the 
exception  of  the  weight  of  the  pier,  will  be  the  same  as  those  used 
in  designing  the  superstructure. 

For  stability  the  solid  gravity  abutment  must  satisfy  the 
same  conditions  as  those  given  for  piers  in  Art.  136.  For  rein- 
forced-concrete  abutments  the  base  must  satisfy  these  same  con- 
ditions while  the  constituent  parts  of  abutments  are  designed 
as  beams  and  columns. 

Unless  the  abutment  rests  on  rock  or  some  other  unyielding 
material  it  is  not  entirely  satisfactory  to  have  the  resultant 
cut  the  base  just  within  the  middle  third;  it  should  be  close  to 
the  center  in  order  to  give  an  approximately  uniform  pressure 
over  the  whole  base.  This  is  true  for  the  reason  that  a  slight 
unequal  settlement  causes  a  considerable  lateral  movement  at 
the  top,  giving  a  condition  illustrated  in  Fig.  1440.  If  the  back 
face  of  the  abutment  is  vertical  and  at  the  same  time  the  dimen- 
sion e  (Fig.  1430)  is  diminished  by  reinforcing  the  parapet  wall 
with  vertical  rods  near  the  rear  surface,  and  the  footing  is 
extended  and  reinforced  near  the  bottom  as  shown  by  the  dotted 
lines  in  Fig.  143^,  the  pressure  may  be  made  to  strike  the  base 
near  the  center. 

Fig.  144  b  shows  the  design  of  abutment  5  of  the  Beaver  bridge 
of  the  Pittsburgh  and  Lake  Erie  Railroad.  The  unit-pressures 
due  to  the  different  resultants  are  given  in  the  following  table. 


438 


BRIDGE   ABUTMENTS 


CHAP.  XIV 


_  Subgrade 
farft  7,£>00'7bl. 
LL  12,00/0  »    21  f  ,000  x.643 


^  of  Abutment. 

Jo  find  Point  of  Application  of  rrP  "take  Moments   ><3  s 
'about  anv  Point  A. 

-  2,052.000x19.6  +  117,000x43.1 
20.9' 


Weight  of  Earth*  I36.000lb$. 


_t 

Total*  178,000  Ibs. 
178.000*.  643  / 
~lf4,454Ibs.onl. 


Loads  on  Abutment  Foundation- 
Masonr        5006  tons. 


Forces  Shown  in  Diagram 
on 
tment. 


are  those  acting  on 
one-half  of  Abu 


Earth  inside  1070    »• 

Fill  at  Ends      732    » 

Total     I  1,200  tons. 
II,  ZOO  -.-  3/5  =  35.  5  tons  -Averaqe 
Load  per  Pi/e.asiuminq  that  Entire 
Weight  rests  on  Piles. 


FIG.   1446.—  Diagram  of  Forces  Acting  on  North  Abutment  and  its  Foundation. 
Pittsburgh  &  Lake  Erie  Railroad  Bridge  over  Ohio  River  at  Beaver,  Pa.,  1908-10. 


ART.  145 


WING- WALL  ABUTMENTS 


439 


TABLE  1440.    UNIT-PRESSURES  (Fig.  1446) 


No. 

Loading 

Max. 

Min. 

Mean 

I 

Masonry  unloaded,  no  fills. 

2  .  3 

o.o 

1.6 

2 

Masonry  and  fill  at  back 

2    3 

I     C 

I    0 

3 

Masonry,  dead  load,  and  fill  at  back  

2-5 

2.1 

2-3 

4 

Masonry,  dead  load,  live  load,  and  fill  at  back. 

2.7 

2-5 

2.6 

S 

Masonry,  dead  load,  live   load,  and    fill    at 

3-2 

3-o 

3.1 

back  and  front. 

6 

Masonry,  dead  load,  live  load,  fills  back  and 

3-6 

3-2 

3-4 

front,  earth  inside. 

ART.  145.     WING- WALL  ABUTMENTS 

This  type  of  abutment  usually  has  its  wings  parallel  to,  and 
in  the  line  of,  the  face  or  front  wall  of  the  abutment  when  used 
for  street  crossings,  as  shown  in /Fig.  1450;  while  for  river  cross- 
ings the  wings  are  usually  at  an  angle  with  the  front  face.  The 
advantage  of  deflecting  the  wings  in  the  latter  case  is  that  the 
abutment  is  thus  better  protected  from  water  getting  in  behind 
the  same,  and  it  also  allows  the  current  to  pass  with  less  dis- 
turbance. It  is  not  customary  to  extend  the  wings  to  the  toe 
of  the  embankment,  they  being  stopped  some  distance  back  of 
this  point  and  the  material  allowed  to  spill  out  in  front  of  the 
ends.  Where  the  stream  is  liable  to  scour  away  this  material 
it  should  be  riprapped  as  shown  in  Fig.  1456. 

According  to  1  BAKER,  the  proper  angle  of  deflection  for  the 
wings,  for  a  minimum  amount  of  masonry,  will  be  between  25 
and  35  degrees  from  a  line  through  the  front  face  of  the  abut- 
ment, if  the  earth  flowing  around  the  toe  is  to  be  kept  3  or  4 
feet  back  of  this  line.  The  wing  walls  are  designed  as  retaining 
walls.  The  thickness  at  any  point  should  not  be  less  than  0.3 
the  height  at  that  point. 

For  low  abutments  a  solid  section  is  employed.  Fig.  145^ 
illustrates  this  type.  The  exposed  faces  have  steel  reinforce- 
ment as  a  protection  against  cracking  through  expansion  and 
contraction  of  the  concrete  near  the  outside.  Reinforcement 
is  also  placed  just  above  the  pile  foundation  to  distribute  the 
load  more  uniformly  over  the  same.  The  design  of  this  abut- 

1  Masonry  Construction,  tenth  edition,  page  526. 


440 


BRIDGE    ABUTMENTS 


CHAP.  XIV 


ment  would  have  been  improved  if  the  bridge  seat  had  been 
moved  a  short  distance  to  the  right  by  narrowing  and  re- 
inforcing the  parapet  wall,  and  the  footing  had  been  moved  a 
short  distance  to  the  left.  The  only  added  expense  in  so  do- 
ing would  have  been,  in  the  slightly  increased  cost  of  the 
superstructure. 


Section  0-B 


FIG.   145^. — Abutment  of  Peoria  &  Pekin  Union  Railway  over  Illinois  River  at 

Peoria,  111. 

For  high  abutments  the  reinforced-concrete  buttressed 
abutment  will  show  some  economy  over  the  solid  type.  The 
first  structure  of  this  type  was  designed  by  A.  0.  CUNNINGHAM, 
in  1903,  for  a  bridge  on  the  Wabash  Railroad  at  Monticello,  111. 
Figs.  145  d  and  145  e  show  views  of  this  abutment  from  the  front 
and  rear  respectively,  while  Fig.  i45/  shows  a  section  of  the 


ART.  146 


U-ABUTMENTS  AND  T-ABUTMENTS 


441 


same.  As  is  seen  in  these  illustrations  the  abutment  consists  of 
a  floor,  face  wall,  bridge  seat,  parapet  wall  and  buttresses.  For 
stability  this  type  requires  a 
wider  base  than  the  solid  sec- 
tion abutment,  for  here  earth 
filling  instead  of  concrete  con- 
tributes to  a  large  part  of  the 
stability. 

The  design  of  the  buttressed 
abutment  is  similar  to  that  of 
the  buttressed  retaining  wall, 
the  main  difference  being  that 
in  the  former  the  buttresses 
under  the  bridge  seat  serve  to 
carry,  as  columns,  the  weight 
of  the  superstructure,  as  well 
as  acting  as  beams  to  resist 
the  earth  pressure.  For  the 
outline  of,  as  well  as  an  ex- 
ample of,  the  design  of  but- 
tressed .retaining  walls,  see 
TAYLOR  and  THOMPSON'S 
Concrete,  Plain  and  Rein- 
forced. 


.*„. 


15'  O"  ...........  -*i 


FIG.  i45/.  —  Section  of  Reinforced- 
concrete  Abutment. 


ART.  146.    U-ABUTMENTS  AND  T-ABUTMENTS 

The  U-abutment  is  a  special  form  of  the  wing- wall  abutment 
in  which  the  wings  are  parallel  with  the  roadway  or  track.  The 
one  disadvantage  of  this  type  is  that  a  part  of  the  embankment, 
that  outside  of  the  wings,  does  not  receive  any  protection.  This 
lack  of  protection  may  preclude  the  possibility  of  using  this 
type  where  the  water  rises  to  a  level  above  the  foot  of  the  abut- 
ment. On  account  of  the  wings  being  partially  buried  they  do 
not  receive  as  much  pressure  as  those  of  the  wing-wall  abut- 
ment, although  experience  shows  that  the  wedging  action  caused 
by  the  live  load  ' hammering'  the  fill  between  the  walls  exerts 


442 


BRIDGE   ABUTMENTS 


CHAP.  XIV 


_j 

L  _.  A/?"  n"    —  »     i's-i" 

1 

,         „                                                                               ,  :,        r'-'l   fy 
-XJ     f.                                                                   •SK'l/Jv-  .''* 

Of     O\                                         -      fJvf   T* 

1      1 

\    A 

j 

CM 

i    j 

4      1 
^      \ 

$ 

x 
x> 

...^       ! 

/    "K 

xx                /     i  Y  ?• 

^           \i    —  i   ~^  - 

^^      >/     ?1      ^ 

X\               s5?'                  5l           rnco 
Xx          ^l                  ^.l           >^ 

Y 

I    \   i^l 

xxl   I     y    v 

Y/$///£Wfl^f//'^ 

^ 
V     v 

I 

/ 

\                                                                             1  ^^ 

L 

Side    Elevation. 


Plan. 


7 


[W 

IVJO 

II 

I 

/ 

1 

y 

he- 9' II -'--->( 


Half 
Section 


'^-.  io'5"~->\ 
|         Ha)f- 

"A-      I  Front  Elevation 


FIG. 


1460.  —  Typical    Plain    Concrete    U-abutment    Chicago,    Milwaukee    and 
St.  Paul   Railway. 


ART.  146 


U-ABUTMENTS  AND  T-ABUTMENTS 


443 


a  very  considerable  pressure.  If  the  side  walls  are  well  tied  to 
the  face  wall  with  steel  reinforcing  rods,  the  thickness  of  the 
face  wall  may  be  somewhat  decreased.  Fig.  1460  shows  a 
typical  U-abutment. 

Fig.  1466  indicates  a  type  in  which  the  side  walls  are  con- 
nected by  transverse  walls.  In  this  way  the  side  walls  are  made 
to  act  as  beams  of  spans  equal  to  the  distances  between  trans- 
verse walls,  thus  reducing  the  necessary  thickness  of  the  same. 
The  floor  distributes  the  loads  over  a  considerable  area  of  soil 


Half  Sec  tion  A  A .  Half  Rear  Elevation.. 


49-9'  - 
Section  on  <t  Between  Tracks. 


FIG.    1466. — Typical    U-abutment     for    Short    Plate    Girder    Spans,    Milwaukee, 
Sparta,  and  Northwestern  Railway. 

as  well  as  to  bring  the  weight  of  the  filling  into  use  to  develop  a 
high  degree  of  stability.  The  front  wall  was  tied  to  the  side 
walls  with  J-inch  rods.  The  transverse  walls  were  reinforced 
with  twenty-six  f -inch  square  rods  carried  into  the  side  walls  to 
within  i  foot  of  their  outer  surface.  Openings  at  the  bottom  of 
the  transverse  walls  were  provided  for  the  convenience  of 
the  workmen.  Drainage  was  provided  for  by  pipes,  as  shown 
in  the  illustration. 

A  very  satisfactory  way  to  reduce  the  necessary  amount  of 
masonry  in  an  abutment  is  to  do  away  with  as  much  of  the 
earth  pressure  as  possible.  Fig.  1460  illustrates  a  modification 
of  the  U-abutment  in  which  this  was  done  by  making  a  solid 
reinforced-concrete  floor  on  top,  which  carries  the  ballast 


444 


BRIDGE   ABUTMENTS 


CHAP.  XIV 


I  ,«^...  *:;**.,,,.*..£,..*_.. 


I 


fe^'P          <— -3'J«--H        B 


,     Section  A-A 
FIG.   1464:. — Bridge     Abutment     with     Reinforced-concrete     Deck. 


ART.  146 


U-ABUTMENTS  AND  T-ABUTMENTS 


445 


directly,  thus  allowing  the  earth  to  take  its  natural  slope, 
bringing  the  toe  to  the  bottom  of  the  front  face.  In  this 
way  all  earth  pressure  except  the  small  amount  on  the 


FIG.   146^. — Outline  of  Standard  Concrete  Abutment. 

back  curtain  wall  and  back  end  of  the  side  walls  is  done 
away  with.  The  curtain  wall  is  used  to  insure  keeping  the 
outside  fi]l  in  place. 


10 


v. 


7g  obtain  volume -Follow horizontal 
line  indicating  height  to  an  intersection 
with  line  indicating  width  of  abutments, 
thence  along  vertical  line  to  scale  indicat- 
ing volume 


500 


1000 


Volume,  Cu.Yds. 
FIG.   146?. — Diagram  of  Cubature  of  Concrete  Abutments. 

Fig.  146^  shows  the  standard  type  of  abutment  used  on  the 
Harriman  Lines  for  single-track  railroad  structures.  The 
dimensions  of  W,  D  and  B  for  concrete  abutments  are  given  in 


446 


BRIDGE    ABUTMENTS 


CHAP.  XIV 


Table  146 a  (the  dimensions  on  the  diagram  being  mean  values), 
while  the  volumes  of  masonry  for  different  heights  and  widths 
are  given  in  Fig,  1460.  The  projection  of  coping  is  made  4 

40'01 


Cross     Sec-Hon 
A-B. 

FIG.  1467. — Concrete  T-abutment.  South  Bend  & 
Southern  Michigan  Ry.  over  St.  Joseph  River,  near 
Berrien  Springs,  Mich. 

inches  for  stone  masonry  abutments  10  feet 
or  under  in  height,  and  6  inches  for  heights 
over  10  feet.  All  concrete  abutments  have 
a  coping  projection  of  4  inches. 

T- ABUTMENTS. — The  T-abutment  will 
usually  show  some  economy  over  the  U- 
abutment  for  small  heights  and  narrow 
roadways.  Fig.  1467  illustrates  a  skew 
T-abutment  used  on  the  South  Bend  & 
Southern  Michigan  Railway.  In  this 
case  the  foundation  was  hard-pan  and  so  permitted  stepping-up 
of  the  base  of  the  stem.  Another  T-abutment  is  illustrated 
in  Fig.  146$. 


P  Jan. 


ART.  147 


BURIED  ABUTMENTS 


447 


TABLE  No.  1460 
DIMENSIONS  OF  CONCRETE  ABUTMENTS.— HARRIM AN  LINES'  STANDARD,   1906 


Deck  plate  girders 

Span 

20 

30 

40 

5o 

60 

70 

80 

90 

IOO 

W 

16-  8 

17-    I 

17-    2 

17-  4^ 

17-  7 

17-10 

18-  i 

18-  2 

18-  2i 

D 

o-  7 

3-oi\ 

3-9f 

5-iof 

5-nf 

7-9f 

9-3f 

9-  8f 

9-iof 

B 

i-  5 

2-    I 

2-  7 

2-  7 

2-    I 

2-  3 

2-  7 

2-  8 

2-  9 

Through  plate  girders 

Span 

30 

40 

So 

60 

70 

80 

90 

IOO 

W 

1  6-  8 

17-10 

18-  2 

19-  o 

19-10 

19-  6 

19-  8 

I9TIO 

D 

.<'.... 

I-    2 

I-    2 

I-    2 

1-9* 

i-9i 

2-Iof 

2-  1  Of 

2-Iof 

B 

2-    I 

2-  3 

2-  3 

2-  3 

2-  3 

2-  7 

2-  9 

3~  o 

Through  riveted  trusses 

Through  pin  trusses 

Span 

IOO 

no 

I2S 

140 

150 

ISO 

1  60 

180 

200 

W 

20-  o 

20-  o 

20-  o 

20-  8 

21-    2 

21-2 

21-    2 

21-  4 

21-  4 

D 

4-  of 

4-  of 

4-  of 

4-  of 

4-  of 

4-  of 

4-  of 

4-  of 

4-  of 

B 

2-1  1 

3-  o 

3-  i 

3-  3 

3~  4 

3~  i 

3-  i 

3-  9 

3-6 

Note:  All  distances  are  expressed  in  feet  and  inches. 


ART.  147.     BURIED  ABUTMENTS 

Instead  of  placing  the  abutment  at  the  edge  of  the  stream  it  is 
sometimes  set  back  in  the  embankment  and  the  latter  allowed  to 
spill  out  in  front  of  the  same  up  to  the  bridge  seat.  In  this  case 
most  of  the  earth  pressure  back  of  the  abutment  will  be  balanced 
by  that  in  front,  and  hence  a  much  less  massive  abutment  is 
required.  On  the  other  hand,  a  greater  length  of  superstructure 
is  required.  In  some  cases  in  addition  to  the  buried  abutment 
a  pier  is  placed  at  the  foot  of  the  embankment,  in  which  case 
the  buried  abutment,  a  pier  and  a  short  span  take  the  place  of 
the  regular  abutment. 

The  buried  abutment  of  the  East  Haddam  bridge  across  the 
Connecticut  River  at  East  Haddam,  Conn.,  which  supports  a 
99-foot  deck  span,  consists  of  two  reinforced- concrete  columns, 
two  footings  and  a  transverse  slab,  as  illustrated  in  Fig.  14 ja. 
The  footings  are  tied  together  with  four  i-inch  rods  encased  in 
concrete.  The  transverse  reinforced-concrete  slab  15  inches 
thick  and  6  feet  deep  connects  the  tops  of  the  columns  and  keeps 
the  earth  filling  from  the  bridge  seats,  which  rest  on  the  columns. 


448 


BRIDGE   ABUTMENTS 


CHAP.  XIV 


A  stone  slope  pavement  protects  the  bottom  of  the  filling, 
which  is  carried  up  around  the  columns  to  within  about  6  inches 
of  the  bridge  seats. 

The  buried  abutment  for  a  bridge  on  the  Louisville  &  Nash- 
ville Railroad  is  illustrated  in  Fig.  147^  It  consists  of  two 
shafts;  a  curtain  wall  connecting  them;  a  spread  footing; 


— ^J  'A?§  :5Goncrete 


JL 


Half  Plan 


Girder  G 


FIG.   1470. — A  Buried  Abutment. 

seats;  parapet  and  side 
walls.  The  shafts  are  4  feet 
thick,  3  feet  1 1  inches  wide  at  the 
top  and  14  feet  wide  at  the  bot- 
tom. They  are  5  feet  apart  in 
the  clear  and  are  connected  by  a 
7-inch  curtain  wall.  Wing  buttresses,  varying  from  6  to  15 
inches  in  thickness  and  from  o  to  4  feet  6  inches  in  width,  stiffen 
the  shafts  and  transfer  some  of  the  load  to  the  footing.  The  toe 
end  of  the  footing  is  reinforced  near  the  lower  surface,  and  the 
heel  end  is  reinforced  near  both  the  lower  and  upper  surfaces. 
The  parapet  and  side  walls  are  both  13  inches  thick.  The  chief 
function  of  the  side  walls  is  to  start  the  embankment  slope  far 


ARI.  148 


REINFORCED  ARCH  ABUTEMNTS 


449 


enough  back  to  clear  the  bridge  seats.  An  interesting  descrip- 
tion of  various  methods  of  accomplishing  this  is  given  in  an 
article  by  C.  M.  LUTHER  in  Engineering  News,  vol.  70,  page 
816,  Oct.  23,  1913. 


-3-10*— *\ 


24-0"- 

S/de  E/evation.  Front Elevation 

FIG.   1476. — Reinforced-concrete   Buried  Abutment,  Louisville  &  Nashville  R.  R. 
Bridge  over  Cumberland  River. 


ART.  148.     REINFORCED  ARCH  ABUTMENTS 

The  reinforced  arch  abutment  may  be  considered  as  a  modifi- 
cation of  the  U- abutment.  Among  the  first  abutments  of  this 
type  were  those  for  a  bridge  of  the  Illinois  Central  Railroad  over 
the  Ohio  River  at  Cairo,  111.,  designed  by  W.  M.  TORRANCE 
under  the  direction  of  F.  H.  BAINBRIDGE.  As  shown  'in  Fig. 
29 


45° 


BRIDGE   ABUTMENTS 


CHAP.  XIV 


1480  the  abutment  consists  of  face  and  side  walls,  an  arched  slab 
at  the  top,  another  about  halfway  down,  and  still  another  at  the 
bottom.  The  earth  fill  is  distributed  so  as  to  give,  in  conjunc- 
tion with  the  other  forces,  a  nearly  uniform  bearing  over  the  base 
of  the  abutment. 

%»^-"--^=^\  ggg 
x 


Longitudinal     Section.  Section      A-B. 

The  Chicago,  Milwaukee 
&  St.  Paul  Ry.,  has  done 
much  in  developing  the 
reinforced  arch  abutment. 
Fig.  1486  illustrates  the 
abutments  of  a  bridge 
near  Lombard,  Montana. 
This  abutment  is  said  to 
be  more  representative  of 
a  stage  in  the  development 
of  abutment  design  than  a 

developed  type.  Fig.  148^  represents  a  type  which  is  adopted 
as  a  standard  on  that  Road.  The  shafts  rest  on  independent 
concrete  footings  and  are  braced  by  longitudinal  and  trans- 
verse reinforced- concrete  braces.  The  floor  system  is  composed 
of  slabs  and  beams,  the  latter  running  transversely  and  carry- 
ing their  loads  to  the  opposite  pairs  of  shafts  and  to  the  longi- 
tudinal arched  beams  at  a  point  midway  between  the  shafts, 


Plan. 


FIG.  i49a. — Reinforced-concrete  Arch 
Abutment. 


FIG.  148^. — Reinforced-concrete    Arch    Abutment    of    Lind    Viaduct,    Chicago, 
Milwaukee,  and  St.  Paul  Railway.     Built  in  1909. 


ART.  148 


REINFORCED    ARCH    ABUTMENTS 


451 


thus  making  the  beam  spacing  8  feet  center  to  center,  the  shaft 
spacing  longitudinally  being  16  feet  center  to  center. 

For  valuable  material  on  the  design  and  costs  of  various  types 
of  abutments  see  a  paper  by  J.  H.  PRIOR  in  Proceedings  of  Amer- 
ican Railway  Engineering  Association  (1912),  vol.  13,  page 
1085,  as  well  as  an  article  by  W.  M.  TORRANCE  on  The  Design 
of  High  Abutments,  in  Engineering  News,  vol.  55,  page  36, 
Jan.  ii,  1906. 


CHAPTER  XV 

SPREAD  FOUNDATIONS 

ART.  149.     GENERAL  CONSIDERATIONS 

Foundations  for  buildings,  where  bedrock  is  some  distance 
below  the  surface,  are  of  three  general  types :  First,  those  carried 
deep  to  rock  or  hard-pan;  second,  those  in  which  piles  are  used; 
and  third,  those  spread  over  a  given  surface.  The  first  type  is 
widely  used  for  heavy  buildings  where  the  material  overlying  the 
rock  is  soft,  and  is  exemplified  in  the  pneumatic-caisson  process 
described  in  Chap,  X,  and  in  the  open- well  process  described 
in  Chap.  XI.  Although  the  most  expensive  type  of  founda- 
tion, it  offers  the  advantage  of  an  absolutely  unyielding  support 
for  the  buildings.  The  silbject  of  bearing  piles  is  treated  in 
Chaps.  I  to  V  inclusive. 

The  object  of  the  shallow  type  of  foundation  is  to  spread  the 
Joad  over  a  considerable  horizontal  area  near  the  surface  of  the 
ground;  that  of  pile  foundations  to  distribute  the  load  over  a 
considerable  vertical  area — the  circumferential  surface  of  the 
piles — as  well  as  carrying  some  of  it  to  the  horizontal  stratum  at 
the  feet  of  the  piles;  while  the  deep  foundation  distributes  the 
load  over  a  relatively  small  area  on  the  rock  or  hard-pan.  Where 
rock  is  present  near  the  surface  there  is  no  foundation  problem, 
it  being  necessary  only  to  level  off  the  rock  with  a  layer 
of  concrete  and  place  the  columns  or  walls  directly  upon  it, 
although  a  spread  footing  may  be  used  where  the  foundation 
loads  are  very  heavy. 

In  many  localities  the  most  common  type  for  light  buildings 
is  the  shallow  foundation,  and  in  modern  development  it  is 
being  used  to  a  considerable  extent  for  heavy  structures.  In 
its  original  and  simplest  form  the  shallow  foundation  consists 
of  a  wide  concrete  or  masonry  footing  with  its  maximum  area  at 

452 


ART.  150 


EARLY  TYPES   OF   FOOTINGS 


453 


the  base  and  stepped  off  to  decrease  in  horizontal  area  toward  the 
top,  the  latter  being  of  sufficient  size  to  form  a  seat  for  the  wall 
or  column  base.  Although  this  makes  a  satisfactory  footing  for 
small  loads  it  is  not  well  adapted  to  heavy  loads  owing  to  the 
depth  required  to  get  the  necessary  spread  of  base.  Other  forms 
of  shallow  foundations  have  been  developed,  such  as  the 
wooden  grillage,  the  inverted  arch,  the  steel  I-beam 
grillage,  and  the  reinforced-concrete  spread  footing,  all  of 
which  require  less  depth. 

The  shallow  type  of  foundation  is  relatively  inexpensive, 
and  easily  and  quickly  constructed,  but  it  possesses  the  disad- 
vantage of  failing  to  furnish  a  rigid  and  unyielding  support  for 
the  building.  Where  founded  on  compact  sand  the  settlement 
will  be  slight,  seldom  more  than  ^  inch,  but  where  founded  on 
a  material  like  the  Chicago  clay  the  settlement  may  in  time 
amount  to  2  feet  or  more.  Hence  heavy  buildings  resting  on 
shallow  foundations  are  built  to  allow  for  a  certain  amount  of 
settlement,  or  else  the  foundations  are  so  constructed  that 
powerful  hydraulic  jacks  can  be  used  to  raise  the  building  to 
permit  shimming  up.  Uniform  settlement  causes  but  little 
trouble  and  can  be  easily  taken  care  of;  but  unequal  settlement 
causes  the  walls  to  crack.  The  most  satisfactory  method  of 
guarding  against  unequal  settlement  was  early  found  to  be  the 
use  of  independent  footings  for  the  columns,  the  area  of  the  base 
of  each  footing  being  so  proportioned  that  the  unit-pressure  is 
the  same  under  all  footings. 


ART.  150.    EARLY  TYPES  OF  FOOTINGS 

MASONRY  FOOTINGS. — This  type,  which  was  one  of  the 
earliest,  is  still  the  standard  for  light  loads.  It  may  be  built  of 
concrete,  brick  masonry,  or  stone  masonry,  the  first  being  the 
most  widely  used  at  present.  In  designing  the  footing  the  area 
of  base  is  found  by  dividing  the  wall  load  by  the  safe  bearing 
power  of  the  soil  as  given  in  Art.  179.  To  safeguard  the 
masonry  against  crushing  the  compressive  unit-stress  on  any 
horizontal  section  should  not  exceed  the  values  given  in  Table 


454  SPREAD   FOUNDATIONS  CHAP.  XV 

1500.     The  top  of  the  footing  is  made  a  little  larger  than  the 
column  base  or  wall. 

Having  'determined  the  top  and  bottom  areas  of  the  footing 
the  next  step  is  to  design  the  offsets,  which  fix  the  depth  of  the 
footing.  As  usually  designed  these  offsets  are  assumed  to  act 
as  free  cantilevers,  and  so  the  allowable  offset  of  any  section 
will  depend  upon  :  First,  the  pressure  on  the  under  side;  second, 
the  transverse  strength  of  the  masonry;  and  third,  the  thick- 
ness of  the  course.  The  center  of  gravity  of  the  base  should 
coincide  with  the  axis  of  ^the  load,  otherwise  additional 
stresses  will  develop. 

TABLE  1500 

Safe  corn- 

Character  of  masonry  pression,  Ibs. 

per  sq.  inch 
Common  brick,  hard  burned  (portland  cement  mortar)  ____  200 

Common  brick,  ordinary  (portland  cement  mortar)  ........  175 

Rubble  masonry,  uncoursed  (portland  cement  mortar)  .....  140 

Rubble  masonry,  coursed  (portland  cement  mortar)  .......  200 

Portland  cement  concrete,  1-2-4  mixture  .................  450 

Portland  cement  concrete,  1-2^-5  mixture  ...........  .....  350 

Portland  cement  concrete,  1-3-6  mixture  .................  250 

Considering  the  case  of  a  footing  for  the  wall  of  a  building, 
let  p  denote  the  unit-pressure  in  pounds  per  square  foot  on  the 
bottom  of  the  course  in  question;  R,  the  modulus  of  rupture  of 
the  masonry;  /,  the  factor  of  safety  used;  /,  the  thickness  of  the 
course  in  inches;  and  o,  the  allowable  offset  of  the  course  in 
inches.  The  following  formula  is  then  obtained, 


A  factor  of  safety  of  about  six  will  usually  be  advisable.  In 
designing  masonry  footings  for  columns  the  method  given  in 
Art.  158  is  recommended,  although  the  above  formula  may  give 
sufficient  precision. 

OTHER  EARLY  TYPES  OF  FOOTINGS.  —  Owing  to  its  lack  of 
transverse  strength  masonry  is  ill-adapted  to  take  loads  which 
cause  flexural  stresses  of  any  magnitude.  For  this  reason  vari- 


ART.  150 


EARLY  TYPES   OF  FOOTINGS 


455 


ous  substitutes  have  been  adopted,  the  idea  being  to  use  some 
material  having  considerable  transverse  strength  in  order  to 
reduce  the  necessary  depth. 

Among  the  early  types  was  the  timber  grillage.  This  con- 
sists of  two  or  more  layers  of  heavy  timbers,  each  layer  being 
placed  at  right  angles  to  the  one  above  and  below,  the  top  and 
bottom  being  often  sheathed  with  a  layer  of  planking.  The 
___  .Average  Ground  Line  various  courses  are  well  tied 

together  with  drift  bolts. 
Examples  of  such  grillages 
have  been  dug  up  after  being 
buried  from  50  to  100  years 
and  where  below  ground- 
water  level  have  been  found 
to  be  in  a  perfect  state  of 


7'Oc-h  - 


-9'0ct- 


Concrete  Piles  -  -~- 


FIG.   i5oa. — A  Typical  Masonry  Footing. 


FIG. 


1506. — Spread  Footing  of 
Timber  Column. 


preservation.  The  high  price  of  timber,  together  with  its  rela- 
tively low  transverse  strength  and  the  uncertainty  of  the  future 
ground-water  level,  makes  timber  an  undesirable  material  for 
use  in  permanent  foundations.  For  temporary  structures,  such 
as  exposition  buildings,  it  is  still  used  to  some  extent.  Fig. 
150^  and  Fig.  150^  show  the  details  of  such  a  grillage  when 
used  under  columns. 

Another  type,  which  was  employed  in  some  of  the  early 


456 


SPREAD    FOUNDATIONS 


CHAP.  XV 


heavy  Chicago  buildings,  consisted  of  a  thick  concrete  platform 
continuous  over  the  whole  area  of  the  building  site,  forming  a 


1 


4-  "*  width  of  birder s 
supported.  Under  a// 
(j/rders  these  P/'eces  ran 
•down  to  Footing. 

I k" Bolt 


FIG.   150*7. — Braced  Column  Footing. 


FIG.   i sod. — Footing  of  Inverted  Masonry  Arch,  Drexel  Building,  Philadelphia,  Pa. 

deep  monolithic  slab  at  the  cellar-floor  level  and  on  which  the 
columns  and  walls  rested.     The  effect  of  variation  in  the  magni- 


ART.  151          MODERN  TYPES  OF  SPREAD  FOUNDATIONS  457 

tude  of  the  concentrated  loads  was  to  crack  the  concrete  bed  into 
a  number  of  independent  footings  and  this  was  naturally  fol- 
lowed by  great  irregularity  in  the  settlement  of  various  parts  of 
the  building.  Hence  this  form  of  footing  was  never  entirely 
satisfactory. 

Another  early  type  of  spread  foundation  was  that  of  the 
inverted  masonry  arch  which  was  first  used  in  the  Drexel 
Building,  Philadelphia,  Pa.,  built  in  1893,  the  details  of  which 
are  shown  in  Fig.  150  d.  Another  notable  example  of  the  use  of 
this  type  was  in  the  World  Building,  New  York  City.  Both 
of  these  structures  were  among  the  early  examples  of  the  modern 
steel  office  building.  In  the  Drexel  Building  the  arches  were 
made  of  brick,  which  distributed  the  column  loads  through  con- 
tinuous lines  of  concrete  bases  in  the  column  rows,  on  the  soil 
below.  Although  the  brick  masonry  arch  is  no  longer  used,  the 
principle  is  still  employed  in  the  reinforced-concrete  arch  footing 
described  in  Art.  159. 

ART.  151.     MODERN  TYPES  OF  SPREAD  FOUNDATIONS 

The  two  modern  types  of  spread  foundations  are  the  steel 
I-beam  grillage  and  the  reinforced-concrete  spread  footing. 
The  steel  I-beam  grillage  dates  back  to  the  types  described  in 
the  preceding  article;  but  since  it  is  still  a  standard  type  it  is 
here  described.  The  conditions  surrounding  its  development 
are  as  follows:  In  the  business  district  of  Chicago  the  soil  con- 
ditions are  peculiar,  made  ground  extending  to  a  depth  of  about 
14  feet  below  street  grade  while  below  that  occurs  a  stratum  of 
hard  stiff  clay  6  to  12  feet  thick.  Below  this  the  clay,  while 
having  the  same  general  characteristics  as  that  above,  becomes 
softer  and  remains  so  to  a  depth  of  75  feet  or  more.  The  upper 
stiff  clay  makes  a  first-class  foundation  bed,  but  the  softer  clay 
below  offers  little  supporting  power. 

After  the  great  Chicago  fire  most  of  the  new  buildings  were 
founded  on  masonry  footings  which  rested  on  this  hard  clay 
stratum.  Owing  to  the  rapid  increase  in  the  size  and  weight 
of  buildings  it  became  necessary  to  increase  the  area  of  the  base 


458  SPREAD   FOUNDATIONS  CHAP.  XV 

of  footings  and  this  in  turn  compelled  the  use  of  deeper  footings. 
As  the  bearing  power  of  the  soft  clay  below  the  hard  stratum  was 
small  the  only  practicable  method  of  obtaining  this  greater 
depth  was  to  extend  the  footing  up  into  the  cellar;  and  thus  the 
cellars  soon  became  filled  with  pyramids  of  masonry,  robbing 
them  of  valuable  space.  This,  together  with  the  fact  that  the 
masonry  footings,  on  account  of  their  large  mass,  formed  too 
large  a  proportion  of  the  total  load  and  were  expensive,  started 
the  search  for  a  better  type  of  footing  for  heavy  loads.  The 
type  thus  developed  consisted  of  crossed  layers  of  old  steel 
rails,  which  were  soon  superseded  by  steel  I-beams,  both 
shapes  being  thoroughly  embedded  in  concrete  as  a  protec- 
tion against  rust. 

Probably  the  first  building  in  America  to  be  built  on  a  steel 
grillage  foundation  was  the  Montauk  Block,  Chicago,  built  in 
1878,  and  designed  by  BURNHAM  and  ROOT,  architects.  The 
ordinary  masonry  footing  was  used  for  a  part  of  the  building,  but 
to  obtain  space  for  the  boiler  a  grillage  of  steel  rails  embedded  in 
concrete  was  used  in  one  part  of  the  cellar.  Soon  after  this  date 
the  price  of  steel  I-beams  dropped  sufficiently  to  make  them 
available  for  this  purpose.  On  account  of  their  larger  section 
modulus  for  any  given  weight  per  foot,  they  are  much  more 
economical  than  rails,  and  in  a  short  time  I-beams  were  adopted 
exclusively.  For  very  heavy  loads  built-up  girders  are  often 
used  in  place  of  I-beams. 

ART.  152.     CONSTRUCTION  OF  I-BEAM  GRILLAGES 

In  the  construction  of  I-beam  grillages  two  or  more  tiers  are 
used,  the  exact  number  depending  on  the  desired  spread  of  base. 
Each  tier  is  placed  at  right  angles  to  the  one  below  it  and  the 
load  is  carried  to  the  soil  through  beam  action.  The  individual 
beams  of  each  tier  should  be  held  in  place  by  cast-iron  or  gas- 
pipe  separators,  preferably  the  former.  These  separators 
should  be  placed  near  each  end  of  the  beams  and  at  intermediate 
positions  not  over  5  feet  apart.  The  beams  should  be  spaced  so 
as  to  give  a  clearance  of  not  less  than  3  inches,  in  order  that  the 


ART.  153  DESIGN  OF  I-BEAM  GRILLAGES  459 

concrete  may  readily  be  filled  in  between  the  beams;  and  not 
more  than  one  and  one-half  times  the  width  of  the  flange,  in 
order  to  reduce  the  stresses  in  the  concrete  filling.  The  latter 
requirement  cannot  always  be  met. 

Concrete  should  be  filled  in  between  the  beams  and  also 
placed  around  the  sides,  top,  and  bottom  of  the  grillage.  The 
thickness  of  the  bottom  layer  should  not  be  less  than  1 2  inches, 
and  the  top  and  sides  should  have  a  protective  coating  of  at 
least  4  inches  net  thickness.  If  portland  cement  concrete  is 
used  the  mixture  should  not  be  leaner  than  1-3-6.  A  layer  of 
cement  grout  of  from  |  to  i  inch  in  thickness  should  be  placed 
between  the  tiers  of  beams. 

ART.  153.    DESIGN  OF  I-BEAM  GRILLAGES 

In  designing  a  grillage  the  area  of  the  column  base  and  the 
column  load  will  be  known  in  advance.  The  grillage  will  be 
designed  for  the  same  load  that  is  used  for  the  base  of  the  col- 
umn, namely,  the  total  dead  load  plus  a  certain  percentage  of  the 
live  load,  the  exact  percentage  depending  on  the  kind  of  building 
and  the  number  of  stories.  The  weight  of  the  grillage  itself 
may  usually  be  neglected. 

As  stated  in  Art.  149,  a  moderate  amount  of  settlement  is 
always  to  be  expected,  but  care  should  be  exercised  to  make  this 
settlement  uniform.  To  accomplish  this,  for  any  particular 
case,  the  unit-pressure  on  the  soil  should  be  the  same  for  all 
footings.  This  is  sometimes  difficult  to  obtain  on  account  of  the 
very  considerable  difference  in  the  proportion  of  live  to  dead  load 
for  different  columns. 

Engineers  agree  that  it  is  essentially  the  dead  load  that  causes 
the  settlement :  First,  because  it  always  acts  with  its  maximum 
intensity;  and  second,  because  it  is  the  first  loading  that  comes 
on  the  foundation.  Unequal  settlements  during  erection  due  to 
dead  load,  are  also  troublesome  in  the  case  of  steel  buildings  on 
account  of  the  difficulties  involved  in  fitting  together  the  various 
members  of  the  superstructure.  For  the  above  reasons  most 
engineers  design  footings  for  equal  unit-pressures  under  dead 
load,  or  under  dead  plus  partial  live  loads. 


460  SPREAD  FOUNDATIONS  CHAP.  XV 

In  Table  153^  the  results  are  tabulated  for  the  design  of 
footings  for  an  actual  structure  by  using  four  formulas  that  are 
employed  in  current  practice.  Let  D  denote  the  dead  load  on 
the  base  of  any  column  footing;  T,  total  load  on  same  footing; 
H,  the  dead  load  plus  one-half  the  probable  live  load  on  the 
same  footing;  Df,  the  dead  load  on  the  base  of  the  critical  col- 
umn footing;  Z",  the  total  load  on  the  base  of  the  critical  col- 
umn footing;  H' ',  the  dead  load  plus  one-half  the  probable  live 
load  on  the  base  of  the  critical  column  footing;  B,  the  safe  unit 
bearing  value  of  the  soil;  and  A,  the  area  of  bearing  of  base  of 
column  footing  for  that  column  in  which  D  denotes  the  dead 
load.  The  formulas  are  as  follows: 

McCullough,  A=DTf/(BDr) 

Schneider,  A=DT'/(BDf) 

Moran,  A=HT'/(BHf) 

Live  +  Dead  A  =  T/B 

The  McCullough  formula  gives  uniform  unit-pressure  under 
dead  load,  and  of  a  value  which  makes  the  pressure  under  that 
footing  having  the  minimum  ratio  of  live  to  dead  load  equal 
to  the  safe  bearing  value  of  the  soil.  Thus  the  critical  column 
footing  in  this  formula  is  the  one  having  the  minimum  ratio  of 
live  to  dead  load. 

The  Schneider  formula  gives  uniform  unit-pressure  under 
dead  load,  and  of  a  value  which  makes  the  pressure  under  that 
footing  having  the  maximum  ratio  of  live  to  dead  load  equal  to 
the  safe  bearing  value  of  the  soil.  Thus  the  critical  column 
footing  in  this  formula  is  the  one  having  the  maximum  ratio  of 
live  to  dead  load. 

The  Moran  formula  differs  from  Schneider's  only  in  that 
equal  unit-pressures  occur  under  dead  plus  one-half  probable 
live  load.1  The  other  formula  is  self  evident. 

1  DANIEL  E.  MORAN  explains  the  meaning  of  probable  live  load  as  follows: 
"  The  maximum  probable  load  is  the  load  which  in  the  opinion  of  the  designer  will 
actually  come  upon  the  footings,  and  is  to  be  determined  by  a  study  of  the  con- 
ditions which  will  obtain  when  the  building  is  occupied.  For  instance,  in  a  school- 
house  the  number  of  children  in  each  class  room  and  the  weight  of  desks,  chairs, 
etc.,  may  be  determined  with  considerable  accuracy  and  these  loads  will  make 


ART.  153 


DESIGN  OF  I-BEAM   GRILLAGES 


461 


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10  O   O 


1.8 

8.8. 


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II  II  II  II  II  II 


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462 


SPREAD   FOUNDATIONS 


CHAP.  XV 


The  weak '  element  of  the  McCullough  formula  is  that 
although  it  gives  under  dead  load  the  same  unit-pressure  for 
all  foundations,  yet  for  column  No.  24  it  gives  a  pressure  of 
8580  pounds  per  square  foot  for  dead  plus  one-half  live  load  and 
10  740  pounds  per  square  foot  for  dead  plus  live  load,  both  of 
which  are  dangerously  high  when  compared  to  a  safe  value  of 

7000  pounds  per  square 
foot.  The  Schneider  for- 
mula, which  also  gives 
under  dead  load  the  same 
unit-pressure  for  all  found- 
ations, and  a  maximum 
dead  plus  live-load  pres- 
sure of  7000  pounds  per 
square  foot,  is  very  con- 
servative. Neither  of 
these  two  formulas  gives 
any  consideration  to  the 
live  load  in  causing  settle- 


  -r  A 

i 

4i 

Q 

n 

1 

-¥ 

• 

-L_ 

,      J 

i 

!  ! 

j  I 

sl    r 

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i  ; 

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L  ' 

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—  --J'  6"-— >k—  3'  0" 
- —lO'O- 


ment.     MORAN'S  formula 
==t       ""I  seems  better  in  this  respect 

since  it  recognizes  the  in- 

FIG.   1530. — Steel   I-Beam   Grillage   for   a 

Single  Column.  fluence  of  the  probable  live 

load  and  gives  to  it  one- 
half  the  weight  that  is  given  the  dead  load.  In  it  the  unit- 
pressure  for  dead  plus  one-half  probable  live  load  is  so 
chosen  that  the  maximum  pressure  under  dead  plus  live  load 
equals  the  safe  bearing  power  of  the  foundation  bed.  The  dead- 
plus-live-load  formula  gives  entirely  too  much  weight  to  live 
load,  as  is  seen  from  the  large  variation  in  the  dead-load  stresses. 
For  a  further  discussion  on  this  subject  see  Engineering  News, 
vol.  69,  page  463,  March  6,  1913,  and  page  687,  April  3,  1913. 

the  maximum  probable  live  load.  As  a  further  illustration,  in  many  school- 
houses  there  is  an  assembly  room  which  is  only  used  when  the  class  rooms  are 
vacant  and  consequently  if  class-room  loads  are  used  assembly-room  loads  should 
be  omitted  or  vice  versa;  the  greater  one  of  these  loadings  to  be  used  for  the  prob- 
able load."  A  full  explanation  of  his  method  may  also  be  found  in  the  revised 
edition  of  KIDDER'S  Architects'  and  Builders'  Pocket  Book. 


ART.  153 


DESIGN   OF  I-BEAM   GRILLAGES 


463 


In  designing  steel  grillage  foundations  the  following  assump- 
tions are  made  :  First,  the  pressure  from  the  footing  is  uniformly 
distributed  over  the  bed;  second,  the  pressure  of  one  tier  of 
beams  on  another  is  uniformly  distributed  over  the  latter;  third, 
each  tier  acts  independently  of  all  other  tiers;  and  fourth,  the 
concrete  filling  and  covering  carries  no  stress,  acting  merely  as 
a  protection  against  corrosion. 

For  the  single-column  grillage  the  square  base.  is  the  most 
economical  shape.  Where  the  possible  width  is  restricted, 
as  in  the  case  of  wall-column  footings,  the  grillage  should  be 
made  as  nearly  square  as  possible.  Economy  also  results  in 
using  a  minimum  number  of  tiers. 

EXAMPLE  OF  DESIGN  OF  SINGLE-COLUMN  FOOTING.  —  Load=6oo  ooo  Ibs. 
Allowable  pressure  on  foundation  bed  =  6000  Ibs.  per  sq.  ft.  Size  of 
column  base  =  3  X4  ft.  Required  area  of  base  =  600  000/6000=  100  sq.  ft. 
A  base  10  ft.  square  is  adopted.  Assume  two  tiers  of  beams.  For  the 
top  tier,  the  maximum  bending  moment  M  =  (600  000/4)  (5  —  2)12  = 
5  400  ooo  Ib.  -in.  Using  16000  Ibs.  per  sq.  in.  as  the  safe  unit-stress  in 
the  outer  fiber,  the  total  section  modulus  required  =  I/e  =  5  400  000/16  ooo 
=  337  in3.  Trying  various  combinations  of  beams,  the  following  results 
are  obtained: 


No. 

Number 
of  beams 

I/e  re- 
quired 

Size  of  beam 

I/e  fur- 
nished 

Width 
of  flange 

Clear- 
ance 

i 

3 

112.3 

2o"-65  Ib. 

117.0 

6.25  in. 

8.6  in. 

2 

4 

84.2 

i8"-55  Ib. 

88.4 

6.00  in. 

4  .  o  in. 

3 

5 

67.4 

i5"-55  Ib. 

68.1 

5-75  in. 

i  .  8  in. 

The  choice  lies  between  Nos.  i  and  2,  since  No.  3  does  not  give 
sufficient  clearance.  The  weight  favors  No.  i,  being  250  pounds 
lighter,  while  No.  2  gives  a  more  satisfactory  clearance  and  has 
less  depth,  thus  saving  on  concrete  rilling  and  also  on  excavation 
work. 

Cost  of  250  Ibs.  of  steel  at  2\  cents  ....................  $6.25 

Cost  of  a  2-in.  thickness  of  concrete  ..................  $i  .65 


Amount  saved  by  using  design  No.  i ". $4.60 

For  the  lower  tier:  Max.  M  =  (600  000/4)  (5  —  1.5)12  =  6300000  lb.- 
in.  Total  required  I/e  =  6  300  000/16  000  =  394  in3.  The  following 
results  are  obtained  by  trying  various  combinations  of  beams: 


464 


SPREAD   FOUNDATIONS 


X:HAP.  XV 


No. 


Number 
of  beams 


1 fe  re- 
quired 


Size  of  beam 


I/e  fur- 
nished 


Width 
of  flange 


Clear- 
ance 


1  10  39.4  i2"-4o    Ib.  41.0  5. 21  in.  7.5  in. 

2  12  32.9  i2"-3i|  Ib.  36.0  5. oo  in.  5. 5  in. 

3  14  28.2  i2"-3i|  Ib.  36.0  5. oo  in.  3. 8  in. 

4  16  24.6  io"-25    Ib.  24.4  4. 66  in.  3.0  in. 

The  choice  lies  between  Nos.  2  and  4;  the  latter  has  220  pounds  more 
steel  but  the  clearance  is  better  and  a  2-inch  depth  of  concrete  is  saved^ 

Cost  of  220  Ibs.  of  steel  at  2\  cents $5  -  50 

Cost  of  a  2-inch  thickness  of  concrete. $4 . 50 


Amount  saved  by  using  design  No.  2 $i .  oo 

ART.  154.    DESIGN  or  DOUBLE- COLUMN  FOOTINGS 

Where  the  two-column  loads  are  equal  the  base  of  the  footing 
should  be  rectangular  in  shape  and  symmetrical  about  a  line 


... 

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FIG.   1540. — Double-Column  Footing  of  Steel  I- Beams. 

midway  between  the  columns.  The  total  area  of  the  base  hav- 
ing been  determined  and  the  distance  between  columns  fixed, 
the  proportion  of  length  to  breath  for  the  base  of  footing  should 
be  such  that  the  moment  in  the  lower  tier  of  beams  under  the 
column  centers  equals  that  at  a  point  midway  between  the  col- 


ART.  154  DESIGN  OF  DOUBLE-COLUMN   FOOTINGS  465 

umns.     This  makes   the   three  maximum  moments  approxi- 
mately equal,  and  gives  the  greatest  economy  of  material. 

EXAMPLE  OF  DESIGN  OF  DOUBLE-COLUMN  FOOTING,  EQUAL  LOADS. — 
Column  loads  =500  ooo  Ibs.  Column  spacing=i2  ft.  Allowable 
pressure  on  ground =4000  Ibs.  per  sq.  ft.  Size  of  column  bases =  3^X3 
ft.  Allowable  unit-stress  in  beams  =  16  ooo  Ibs.  per  sq.  in.  To  get  the 
value  x  that  will  make  the  three  moments  equal,  500  000(6  —  x)/2  = 
$ooooox2/2(6+x)  —  500  ooo(yV),  whence  2  =  4.77  ft-  Required  bearing 
area  of  base  =  i  ooo  000/4000=  250  sq.  ft.  Using  a  value  of  x  of  4.75  ft., 
6  =  2507(12+2X4. 7s)  =  n. 63  ft.;  say  11.75.  Let  two  tiers  of  beams 
be  assumed.  Computing  for  top  tier:  Max.  M=  500  000(11.75  — 3)12/8 
=  6  560  ooo  Ib.-in.  Total  required  I/e  =  6  560  000/16  000  =  410  in3. 
After  trying  various  combinations  of  beams,  the  results  are: 

No. 


Number 
of  beams 

I/e  re- 
quired 

Size  of  beam 

I/e  fur- 
nished 

Width 
of  flange 

Clear- 
ance 

3 

136.7 

24"-8o  Ib. 

173-9 

7.0    in. 

10.5  in. 

4 

102.5 

2o"-65  Ib. 

117.0 

6.25  in. 

5-3  in. 

5 

82.0 

i8"-55  lb- 

88.4 

6.0    in. 

3  .  o  in. 

No.  2  will  be  adopted. 

For  lower  tier  the  three  positions  of  maximum  bending  moment  are 
at  the  center  and  4.45  ft.  from  each  end.  M  at  center  =  500  ooo 
(6  —  5.375)12  =  3  750000  Ib.-in.  M  &t,  4.45  ft.  from  the  end= 

[500  ooo     4.452       500  ooo     i.452l 
— .    -  — .    -       -    12  =  3  750 ooo  Ib.-m. 

iQ-75  2  3.5  2    J 

Total  required  7/e  =  3  750  000/16000=234.  Upon  trying  various 
combinations  of  beams,  the  results  are  found  to  be: 


No. 

Number 
of  beams 

I/e  re- 
quired 

Size  of  beam 

I/e  fur- 
nished 

Width 
of  flange 

Clear- 
ance 

i 

12 

iQ-5 

9"-2i  lb. 

18.9 

4-33  in. 

8  .  i  in. 

2 

14 

16.7 

9"-2I  lb. 

18.9 

4-33  in. 

6.1  in. 

3 

16 

14.6 

8"-i8  lb. 

14.2 

4.0    in. 

5  .  i  in. 

4 

18 

13-0 

8"-i8  lb. 

14.2 

4.0    in. 

4.1  in. 

No.  3  will  be  adopted. 

When  the  column  loads  are  not  equal  the  center  of  gravity  of 

the  base  of  the  grillage  is  usually  made  to  coincide  with  the  line 

of  action  of  the  resultant  of  the  two  column  loads  by  making  the 

base  a  trapezoid;  or,  if  the  loads  are  nearly  equal,  it  may  be  done 

30 


466 


SPREAD   FOUNDATIONS 


CHAP.  XV 


by  using  a  rectangular  shape  and  making  the  cantilever  end 
at  the  heavy  load  longer  than  the  other  cantilever  end. 
The  trapezoidal  shape  may  be  obtained  either  by  using  a  larger 
number  of  beams  at  the  heavy  load  end,  or  by  using  the  same 
number  of  beams  and  spacing  them  more  closely  at  one  end  than 
at  the  other.  A  combination  of  the  two  methods  is  sometimes 
used. 


-y^*O/-/"-^L*  I  S\ 


<: 

•i 

-3H 

FIG.   1546. — Steel  I-beam  Grillage  for  Two  Columns  Supporting  Unequal  Loads. 
The  load  on  Column  No.  i  is  500  ooo  Ibs;  that  on  No.  2  is  400  ooo  Ibs. 

If  the  proportions  of  the  base  are  so  fixed  that  the  bending 
moment  under  the  center  of  each  column  equals  that  at  the 
center  of  gravity  of  the  base,  the  three  maximum  moments  in 
the  lower  tier  of  grillage  will  be  closely  equal;  this  condition 
gives  approximately  the  minimum  amount  of  material.  The 
most  satisfactory  method  of  determining  the  dimensions  to 
secure  this  result  is  by  trial. 


ART.  154 


DESIGN  OF  DOUBLE-COLUMN  FOOTINGS 


467 


EXAMPLE  or  DESIGN  OF  DOUBLE-COLUMN  FOOTING,  UNEQUAL  LOADS. — 
Column  loads  and  spacing  as  shown  in  Fig.  154  b.  Allowable  pressure  on 
foundation  bed  =  4000  Ibs.  per  sq.  ft.  Size  of  column  bases  as  shown  in 
Fig.  I54&.  Allowable  unit-stress  in  beams=  16000  Ibs.  per  sq.  in.  Re- 
quired bearing  area  of  base  =900  000/4000  =2  25  sq.  ft.  Distance  from 
Column  No.  i  to  resultant  of  both  column  loads  =  400  000X10/900  000  = 
4-45  ft- 

After  a  few  trials  it  was  found  that  the  moments  under  the 
centers  of  the  two  columns  and  under  the  center  of  gravity  of 
base — line  of  action  of  resultant  of  two  column  loads — were 
approximately  equal  when  ^  =  3.625  ft.,  and  6  =  4.625  ft. 

To  get  b  and  c:  (5+^)18.25/2  =  225  and  (18.25/3)  (&+2c)/(&+c)  = 
3.625+4.45  =  8.075.  Solving  these  two  equations  simultaneously  we 
find  that  approximately  b=  16.6  ft.  and  c  =  8.o  ft. 

Using  two  tiers  of  beams,  the  computations  for  the  upper  tier 
under  Column  No.  i  give: 

Max.  If  =(500000/8)  (14.88  —  3)12  =  8  910000  Ib.-in.  Total  required 
l/e—  557  in3.  After  trying  various  combinations  of  beams,  the  results 
are  as  follows,  and  No.  i  is  adopted: 


No. 

Number 
of  beams 

I/e  re- 
quired 

Size  of  beam 

I/e  fur- 
nished 

Width 
of  flange 

Clear- 
ance 

i 

2 

3 

4 

186.0 
139-5 

24"-9o  Ib. 
24"-8o  Ib. 

186.5 
173-9 

7-13  in. 
7.0    in. 

7.3  in. 
2.7  in. 

For  the  upper  tier  under  Column  No.  2 : 

Max/  M=  (400 000/8)  (10.18-2.75)12  =  4458000  Ib.-in.  Total  re- 
quired 7/6=279  in3.  Trying  various  combinations  of  beams  gives  the 
following  results,  No.  i  being  adopted: 

I/e  fur- 
nished 


No. 


Number 
of  beams 


Clear- 
ance 


7/6  re-      0.       -i  I/e  fur-       Width 

quired      Slze  of  beams      nished       of  flange 

1  3  93.0          i8"-6olb.  93-5        6.10  in.       7.3  in. 

2  4  69.7          i8"-55  Ib.  88.4       6.00  in.       3.0  in. 

In  designing  the  lower  tier  and  running  all  beams  full  length, 
let  #  =  the  distance  from  the  left  end  of  grillage  to  section  in 
question,  the  expression  for  bending  moments  under  Column 
No.  i,  between  the  two  columns,  and  under  Column  No.  2, 
are  respectively  as  follows: 


468 


SPREAD   FOUNDATIONS 


CHAP.  XV 


Jf(col.    No.i) 


4000    x 


(49.8—0.471*)  — 

O 


500000     (%—  2.125): 


M  (between  cols.)  = 


4000   x' 


(49.8  —  o .  47  ix)  —  500  000(2  —  3.625) 


If  (col.  No.  2)  = 


4000   x 


-'(49.8-0.471*)- 

O 


500000(^-3.625)- 


4OOOOO     (X—  12. 25)2 
2.75  2 


To  get  the  values  of  x  for  the  maximum  value  of  M  in  each  of 
the  above  equations  equate  dM/dx  equal  to  zero,  which  gives 
3.42,  8.58  and  13.91  ft.,  respectively.  Substituting  these  three 
values  of  x  in  the  preceding  equations,  the  corresponding  values 
of  M  are,  236000  lb.-in.,  231000  lb.-in.,  and  232000  Ib.-in. 
The  maximum  maximorum  is  therefore  236  ooo  lb.-in.  Total 
required  I/e  =  177  in.3  Trying  various  combinations  of  beams, 
there  is  obtained: 


No. 

Num- 
ber of 
beams 

/Are- 
quired 

Size    of 
beam 

I/e 
fur- 
nished 

Width 
of 
flange 

Clearance 

i 

10 

17.7 

9"-2i    Ib. 

18.9 

4-  33  in. 

5.  9  to  17.  3  in. 

2 

12 

14.7 

8"-2oilb. 

15.0 

4  .  08  in. 

4.3  to  13.  6  in. 

3 

14 

12.7 

8"-i8    Ib. 

14.2 

4  .  oo  in. 

3.1  to  10.9  in. 

U 

16 

II.  0 

7"-i7l  lb- 

II.  2 

3.66  in. 

2.  5  to    9.  3  in. 

No.  4  will  be  adopted. 

Reinforcing  bars  should  be  placed  in  the  concrete  near  the 
upper  surface  for  the  wider  half  of  the  footing. 


ART.  155.     DISTRIBUTION  or  PRESSURE  ON  BASE 

There  is  some  question  regarding  the  error  involved  in  the 
assumption  that  the  pressure  from  the  footing  is  uniformly 
distributed  on  the  ground.  Taking  the  case  of  the  single- 
column  square  footing  it  is  evident  that  the  base  of  the  footing 
will  assume  a  saucer-like  shape,  and  as  a  consequence  the  pres- 
sure will  be  a  maximum  at  the  center  and  a  minimum  at  the 
outside.  The  law  governing  the  variation  of  pressure  will 


ART.  156  STEEL  GRILLAGE  FOUNDATIONS  469 

depend  on  the  relative  deflections  of  different  points  on  the 
base  of  the  footing,  as  well  as  on  the  modulus  of  compressibility 
of  the  soil  and  the  thickness  of  the  compressible  stratum. 
Where  the  modulus  is  low  and  the  thickness  considerable,  the 
slight  difference  in  total  deformation  at  different  points  will 
cause  but  a  slight  difference  in  pressure.  Where  the  soil  is 
compressible  but  inelastic,  or  soft  and  subject  to  lateral  flow, 
a  fairly  uniform  distribution  of  pressure  quickly  obtains. 

Where  the  material  has  a  high  modulus  of  compressibility, 
as  in  shale  or  rock,  the  footing  should  be  designed  for  stiff- 
ness as  well  as  for  strength  or  else  the  surface  of  the  material 
should  be  shaped  to  fit  the  curve  taken  by  the  base  of  the  foot- 
ing when  fully  loaded,  otherwise  the  pressure  will  be  very  un- 
evenly distributed.  For  example,  by  using  a  stress-strain 
diagram  of  the  values  obtained  in  the  foundation  tests  of  the 
St.  Paul  Building,  New  York  City  (see  Engineering  Record, 
vol.  33,  page  388,  May  2,  1896),  a  theoretical  solution  shows 
that  for  the  typical  steel-grillage  footing  the  pressure  varies 
from  a  maximum  at  the  center  to  approximately  zero  at  the 
outside.  The  material  on  which  the  above  foundation  tests 
were  made  consisted  of  very  compact  sand,  while  the  whole 
area  of  the  lot  was  covered  with  a  layer  of  concrete  and  steel 
beams  buried  in  concrete,  the  tests  being  made  through  a  hole. 

ART.  156.     STEEL  GRILLAGE  FOUNDATIONS 

Most  of  the  grillages  used  in  the  foundations  for  the  Phelan 
Building,  San  Francisco,  were  15  feet  square,  and  made  with 
two  cross  tiers  of  I-beams  from  1 8  to  24  inches  in  depth,  or  with 
an  upper  tier  of  built-up  girders  and  a  lower  tier  of  I-beams, 
as  shown  in  Fig.  1560.  The  complete  grillage  plan  is  shown 
in  Fig.  1565. 

1  "All  footings  are  made  with  a  bed  of  concrete  12  inches 
thick  and  12  inches  wider  and  longer  than  the  dimensions  of 
the  first  tier  of  grillage  beams.  In  the  upper  part  of  the  con- 
crete there  are  two  full-length  rectangular  grooves  transverse 

1  Engineering  Record,  vol.  57,  page  366,  March  28,  1908. 


470 


SPREAD   FOUNDATIONS 


CHAP.  XV 


to  the  lower  tier  of  grillage  beams.     In  each  groove  a 
TV-inch  angle  was  carefully  leveled  with  the  upper  edge  of  its 
vertical  flange  truly  horizontal  and  f  inch  above  the  surface 


Boiler  Room  FT 


*!Wr?W*fSH  •  •  '•' 
SubBaseme^  $& 


FIG.   1560. — Footings  with  Plate  Girders  and  I-beams  in  Double  Tiers. 

of  the  concrete.  These  serve  as  leveling  bars  to  receive  the 
lower  flanges  of  the  grillage  beams  and  insure  their  exact  height. 
The  spaces  between  the  beams  and  the  concrete  footings  were 
grouted,  the  second  tier  of  beams  was 
shimmed  f  inch  above  the  top  flanges 
of  the  lower  tier  and  grouted,  the  cast- 
iron  pedestals  were  set  f 
inch  above  the  top  flan- 
ges of  the  distributing 
beams  and  grouted,  and  ^ 
a  solid  mass  of 
concrete  was 


FIG.   1566. — Grillage  Plan  of  Phelan  Building,  San  Francisco,  Cal. 

filled  in  6  inches  around  the  outer  edges  of  the  beams  and 
pedestals  and  up  to  the  cellar  floor,  completely  enclosing  and 
protecting  all  the  substructure  steel  work." 


ART.  156 


STEEL  GRILLAGE  FOUNDATIONS 


471 


Fig.  156^  illustrates  a  very  heavy  grillage  foundation  for 
four  columns  of  the  Curtis  Building,  Philadelphia.  It  was 
necessary  to  use  a  single  grillage  for  the  four  columns  because 
of  the  short  distances  between  the  latter.  The  distributing 
girders  for  Columns  Nos.  254  and  255  have  48XlHnch  webs 


t -IO  -4- 


Q'2'i....jf—  _ 

-- 


FIG.   1 5 6c.— Special   Footing   for   Four    Columns,    Curtis    Building,  Philadelphia. 

reinforced  by  5X3X|-inch  vertical  stifltener  angles  and  two 
13  X  1-inch  vertical  side  plates,  and  the  top  flanges  of  the 
girders  are  connected  by  transverse  tie  plates.  The  column 
loads  are  transmitted  to  the  triple  distributing  girders  by 
bolsters  made  of  solid  slabs  of  plain  square  steel  billets 


472 


SPREAD   FOUNDATIONS 


CHAP.  XV 


which  are  bolted  to  the  upper  flanges  of  the  girders.  The 
concrete  footing  is  reinforced  with  rods  for  part  of  the 
base,  due  to  the  fact  that  the  I-beams  are  there  a  con- 
siderable distance  apart,  thus  developing  beam  action  in  the 
concrete. 


BarctaL 


St 


9  10 


Pbrk  Place 

FIG.   i$6d. — Plan  of  Piers   and  Grillages  for  the  Woolworth    Building. 


The  Woolworth  Building,  New  York  City,  is  founded  on 
solid  rock  115  feet  below  the  curb  level.  The  loads  are  car- 
ried from  the  columns  to  bedrock  through  grillage  footings 
resting  on  reinforced-concrete  piers.  Fig.  156^  shows  the 
general  lay  out  for  the  foundation,  while  1560  shows  some  of 
the  details. 


ART.  156 


STEEL   GRILLAGE   FOUNDATIONS 


473 


474 


SPREAD  FOUNDATIONS 


CHAP.  XV 


ART.  157.  DESIGN  OF  REINFORCED-CONCRETE 
SPREAD  FOUNDATIONS 

Instead  of  serving  merely  as  a  protection  for  the  steel,  con- 
crete may  be  made  to  take  a  part  of  the  load  by  using  a  rein- 
forced-concrete  footing  in  place  of  the  I-beam  grillage,  thus 
lessening  the  cost  of  the  foundation.  Another  advantage  pos- 
sessed by  a  reinforcednconcrete  foundation  is  that  it  can  be 
cast  in  any  shape  or  form  desired.  It  may  be  in  the  form  of  a 
flat  slab  or  of  the  slab-and-beam  type  (Fig.  1590).  The  former 
i  uses  more  concrete,  while  in 

*-  -  ^-3'  0"-  ->H  2' 6"*, 


the  latter  the  form  work  is 
more  expensive.  For  some 
interesting  modifications  of 
the  elementary  type  the 
reader  is  referred  to  Art.  159. 
DESIGN  OF  A  REINFORCED- 
CONCRETE  WALL  FOOTING.  — 
Assuming  the  load  to  be 
64  ooo  pounds  per  linear  foot 
of  wall  and  the  allowable 
bearing  on  the  soil  4000 
pounds  per  square  foot,  the 

width  of  footing  will  be  64000/4000=16  feet.  The  thick- 
ness of  the  wall  is  2  feet  (Fig.  1570).  The  footing  will  be 
designed  at  three  sections,  at  a,  5^  feet  from  the  center  of  the 
wall,  at  b,  3  feet  from  the  center,  and  at  c,  i  foot  from  the 
center.  Taking  a  i-foot  length  of  footing  the  vertical  shears 
and  bending  moments  will  be  as  follows: 

,,.  4000X2.52X12 

Va  =  4000X2^  =  10  ooo  Ib.        Ma=~      --      -  =150  ooo  Ib.-m. 


FIG. 


1570. — Reinforced-concrete  Wall 
Footing. 


Vb  =4000X5   =20ooolb.        Mb=—  —  =  600000  Ib.  -in. 


Vc  =  4000X7   =  28  ooo  Ib. 


Me 


000 


ART.  157     REINFORCED-CONCRETE  SPREAD  FOUNDATIONS 


475 


A  1-2-4  concrete  will  be  used,  with  an  allowable  compressive 
unit-stress1  in  the  concrete  of  fc  =  600  Ibs.  per  sq.  in.  and  an 
allowable  tensile  unit-stress  in  the  steel  of  fs=i6  ooo  Ibs.  per 
sq.  in.  The  ratio  of  the  modulus  of  elasticity  of  steel  to  that  of 
concrete  will  be  assumed  as  ^=15.  The  depth  to  center  of 
steel  rods  necessary  to  give  a  compressive  stress  in  the  concrete 
of  600  Ibs.  per  sq.  in.  is  given  by  the  formula,  d=  ^M/(Rb),  in 
which  R  =  fckj/2.  In  the  latter  formula2  k=  ^2pn-\-(pn)2—pn 

and  j  =  i  -  k/3 ;  p  =  |/y(  ~r  +  i Y     The  work  involved  in  get- 

jc  \njc         / 

ting  the  value  of  R  will  be  greatly  reduced  by  using  the  dia- 
grams found  in  TURNEAURE  and  MAURER'S  Reinforced-Con- 
crete  Construction.  For  the  problem  at  hand  the  value  of 
R  is  95.  Solving  iord,  da  =  V 150 0007(95X1 2)  =  n.$m.',db 
=  V  6000007(95X12)  =23.oin.;andvdc=  V  z  176000/95X12) 
=  32.1  in.  (32^  in.  being  adopted).  As  it  is  inadvisable  to  use 
a  depth  at  any  section  less  than  about  6  inches  the  form  shown 
in  Fig.  157  a  will  be  adopted.  The  steel  in  the  bottom  will  be 
given  a  2 -in.  insulation. 

The  area  of  steel  required  at  each  section  is  given  by  the 
formula,  A=M/(fsjd).  Using  the  values  of  d  obtained  above, 
so  that  the  footing  be  equally  strong  in  tension  and  compression: 

Aa  —    150  ooo/(i6  000X0.88X11. 5)  =  0.92  square  inch, 
Ab  =    600  ooo/(i6  000X0.88X23     )  =  1.85  square  inches, 
Ac  =i  176  ooo/(i6  000X0.88X32.  i)  =  2. 60  square  inches. 

Using  a  rod  spacing  of  3  inches  center  to  center  there  will  be 
4  rods  in  one  foot  of  length  of  the  footing.  The  required  area 
of  each  rod  will  be  2.60/4  =  0.650  sq.  in.  A  lo-inch  square 

1  In  a  wedge-shaped  beam  the  greater  principal  stress  at  the  outer  fibers  acts 
parallel  to  the  upper  surface  of  the  beam  and  with  an  intensity  equal  to  the  maxi- 
mum normal  stress  on  a  vertical  plane  divided  by  cos2**,  in  which  a  is  the  angle 
of  inclination  of  the  upper  surface  of  the  beam;  hence,  the  allowable  bending  unit 
stress  should  be  taken  equal  to  the  safe  compressive  stress  in  the  concrete  multi- 
plied by  cos2  a. 

2  Based  upon  the  assumption  that  the  normal  stress  in  the  concrete  on  any 
vertical  section  varies  as  a  straight  line  and  that  the  stress  in  the  steel  equals 
n  times  the  stress  in  the  concrete.     For  formulas  based  on  a  different  assumption 
see  Proc.  Am.  Soc.  C.  E.,  vol.  39,  page  2067,  Nov.  1913. 


476  SPREAD   FOUNDATIONS  CHAP.  XV 

twisted  rod,  giving  an  area  of  0.660  sq.  in.  will  be  adopted. 
Three  rods  will  furnish  the  required  area  at  b,  while  two  rods  will 
furnish  that  required  at  a;  hence  certain  of  the  rods  may  be 
bent  up  or  cut  off  as  shown  in  Fig.  157^. 

Using  an  allowable  bond  unit-stress  of  140  Ibs.  per  sq.  in. 
of  rod  surface  the  necessary  length  of  rod  to  develop  full  strength 
is  (16  000X0.66)7(140X3. 25)  =  23. 2  in.  Computing  the  bond 
stress  in  the  rods  by  the  formula  lu—(Sd  —  M  tan  a)/(jd2  2o) 
in  which  tan  a  is  the  slope  of  the  upper  surface  of  the  footing 
and  S0  the  perimeter  of  the  rods  at  the  section  in  question,  the 
values  are  as  follows: 


MO  =  (10000X15.4  — !5ooooXo.3i2)/(o.88Xi5.42  X6.5o)  =  7glb./sq.  in. 


ub  =(20000X24.75  — 6oooooXo.3i2)/(o.88X24.752X9.75)  =  59lb./sq.  in. 


uc  =(28000X32.25  —  1  176 000X0.312)7(0.88X32. 252X 13)  =45 lb./sq.  in. 

All  of  these  values  are  well  below  the  safe  limit  of  140  Ibs. 
per  sq.  in. 

Assuming  that  the  concrete  takes  no  longitudinal  tension 
the  maximum  intensity  of  diagonal  tension  is  given  by  the 
formula  t=(Sd—M  tan  a  )/(jd2).  A  shorter  method  of  com- 
puting the  maximum  diagonal  tension  is  by  taking  the  bond 
stress  values  and  multiplying  them  by  the  perimeter  of  the  rods. 
Thus, 

ta  =(79X6.50)712  =  43  Ibs.  per  sq.  in. 
tb  =(59X9-75)712  =  48  Ibs.  per  sq.  in. 
*c  =(45X13.0  )/i2  =  49  Ibs.  per  sq.  in. 

Although  conservative  specifications  limit  the  allowable 
diagonal  tension  to  40  pounds  per  square  inch,  the  above  can 
be  safely  carried  by  the  concrete  without  reinforcement,  but 
to  illustrate  the  method  stirrups  will  be  designed  to  carry  all 
of  this  tension.  Placing  the  stirrups  on  a  45-degree  slope  and 
using  f-inch  square  twisted  rods  with  two  prongs  in  a  1 2-inch 
length,  as  shown  in  Fig.  1570,  the  strength  of  one  line  of 
stirrups  in  a  i2-inch  length  will  be  16  oooX(|-)2X2  =  45  oc 
pounds.  Denoting  the  horizontal  distance  between  rows  of 

1  Only  approximately  true  when  p  is  not  constant. 


ART.  158       REINFORCED-CONCRETE    COLUMN   FOOTINGS 


477 


stirrups  by  s  the  formula  is,  s  =  45007(1 2  X/X cos  45°),  giving 

Sa  =4500/12X43X0.707  =  12  inches. 
Sb  =4500/12X48X0.707  =  11  inches. 
Sc  =4500/12X49X0.707  =  10  inches. 

A  uniform  spacing  of  10  inches  will  be  adopted. 

In  this  type  of  beam  the  maximum  intensity  of  vertical 
shear  occurs  at  the  top  and  equals  fc  tan  a,  where  a  is  the  in- 
clination of  the  upper  surface  of  the  slab.  The  shearing  stress 
is  therefore  600X0.312  =  187  pounds  per  square  inch. 


ART.  158.  DESIGN  OF  REINFORCED-CONCRETE 
COLUMN  FOOTINGS 

The  stresses  in  a  reinforced-concrete  footing  for  a  column  are 
due  more  to  flat-slab  action  than  to  beam  action  and  hence  are 
much  less  determinate  than  in  the 
wall  footing.  However,  the  stresses 
may  be  approximately  analyzed  by 
either  flat-slab  or  beam  formulas. 
The  former  method  is  not  entirely 
satisfactory,  due  partly  to  the  neces- 
sary approximations  of  any  formulas 
based  on  the  theory  of  the*  flat 
plate,  and  partly  to  the  tedious  com- 
putations involved  unless  specially 
prepared  tables  or  diagrams  are  used. 

.          r      .         ,      .  -  FIG.   1580. — Column  Footing  of 

For  an  example  of  the  design  ot   a  Reinforced  Concrete, 

footing  based  on  the  flat-slab  prin- 
ciple see  page  644  of  the  second  edition  of  TAYLOR  and  THOMP- 
SON'S Concrete,  Plain  and  Reinforced. 

Where  beam  formulas  are  used  it  is  generally  assumed  that 
the  section  of  maximum  bending  moment  and  shear  is  at  the 
outer  face  of  the  column.  If  the  footing  has  a  two-way  rein- 
forcement the  stress  cannot  be  uniformly  distributed  over 
this  section.  For  instance,  looking  at  Fig.  158  a,  the  load  from 
the  soil  at  point  c  will  evidently  go  to  the  column  through  dc 


478  SPREAD   FOUNDATIONS  CHAP.  XV 

acting  as  a  cantilever  beam.  On  the  other  hand  a  part  of  the 
load  at  a  will  first  go  to  some  point  as  c  through  ac  acting  as  a 
beam,  and  the  balance  to  some  point  as  b  through  ab  acting  as 
a  beam.  The  part  which  goes  to  c  will  then  go  to  d  through 
cd  acting  as  a  beam,  while  the  part  which  goes  to  b  will  go  to  e 
through  be  acting  as  a  beam.  Thus  it  is  evident  that  the  stress 
along  the  plane  A- A  will  vary  from  a  maximum  at  the  column 
face  to  a  minimum  near  the  sides  of  the  footing. 

From  experiments  made  in  the  testing  laboratory  at  the 
University  of  Illinois,  A.  N.  TALBOT  summarizes  the  proper 
method  of  design  as  follows:  x"For  footings  having  projec- 
tions of  ordinary  dimensions,  the  critical  section  for  the  bending 
moment  for  one  direction  (which  in  two-way  reinforced  con- 
crete footings  is  to  be  resisted  by  one  set  of  bars)  may  be  taken 
to  be  at  a  vertical  section  passing  through  the  face  of  the  pier. 
In  calculating  this  moment,  all  the  upward  load  on  the  rectangle 
lying  between  a  face  of  the  pier  and  the  edge  of  the  footing 
is  considered  to  act  at  a  center  of  pressure  located  at  a  point 
halfway  out  from  the  pier,  and  half  of  the  upward  load  on  the 
two  corner  squares  is  considered  to  act  at  a  center  of  pressure 
located  at  a  point  six- tenths  of  the  width  of  the  projection  from 
the  given  section.  .  .  . 

"With  two-way  reinforcement  evenly  spaced  over  the  foot- 
ing, it  seems  that  the  tensile  stress  is  approximately  the  same 
in  bars  lying  within  a  space  somewhat  greater  than  the  width 
of  the  pier  and  that  there  is  also  considerable  stress  in  the  bars 
which  lie  near  the  edges  of  the  footing.  For  intermediate 
bars  stresses  intermediate  in  amount  will  be  developed.  For 
footings  having  two-way  reinforcement  spaced  uniformly  over 
the  footing,  the  method  proposed,  for  determining  the  maxi- 
mum tensile  stress  in  the  reinforcing  bars,  is  to  use  in  the  cal- 
culation of  resisting  moment  at  a  section  at  the  face  of  the 
pier  the  area  of  all  the  bars  which  lie  within  a  width  of  footing 
equal  to  the  width  of  pier  plus  twice  the  thickness  of  footing, 
plus  half  the  remaining  distance  on  each  side  to  the  edge  of  the 
footing.  This  method  gives  results  in  keeping  with  the  results 

1  Bulletin  No.  67,  Engineering  Experiment  Station,  University  of  Illinois. 


ART.  158       REINFORCED-CONCRETE    COLUMN   FOOTINGS 


479 


of  tests.  When  the  spacing  through  the  middle  of  the  width 
of  the  footing  is  closer,  or  even  when  the  bars  are  concentrated 
in  the  middle  portion,  the  same  method  may  be  applied  without 
serious  error.  Enough  reinforcement  should  be  placed  in  the 
outer  portion  to  prevent  the  concentration  of  tension  cracks  in 
the  concrete  and  to  provide  for  other  distribution  stresses. 

"The  method  proposed  for  calculating  maximum  bond  stress 
in  column  footings  having  two-way  reinforcement  evenly  spaced, 
or  spaced  as  noted  in  the  pre- 
ceding paragraph,  is  to  use  the 
ordinary  bond-stress  formula, 
and  to  consider  the  circumfer- 
ences of  all  the  bars  which  were 
used  in  the  calculation  of  tensile 
stress,  and  to  take  for  the  exter- 
nal shear  that  amount  of  upward 
pressure  or  load  which  was  used 
in  the  calculation  of  the  bending 
moment  at  the  given  section." 
In  the  preceding  discussion  the 
slab  is  assumed  to  have  a  hori- 
zontal upper  surface. 

DESIGN  OF  A  FOUR- WAY  RE- 
INFORCED FOOTING. — A  footing 
with  four-way  reinforcement 
(Fig.  1586)  is  more  susceptible 
of  a  rational  analysis  than  the  two-way  reinforced  foot- 
ing. Tests  by  A.  N.  TALBOT  (see  previous  reference)  show 
that  this  type  gives  a  somewhat  stronger  footing  than  the 
two-way  type. 

Assuming  the  load  to  be  210000  pounds  and  the  allowable 
bearing  on  the  soil  3000  Ibs.  per  sq.  ft.,  the  area  of  the  footing 
will  be  210  000/3000  =  70  sq.  ft.  A  baseS  feet  6  inches 
square  will  be  used.  The  column  base  will  be  assumed  as  20 
inches  square. 

In  this  design  the  part  ABCD  in  Fig.  158  &  will  be  assumed 
to  act  as  a  free  cantilever  about  CD,  as  will  also  ABEF,  ABGH 


FIG.   1586. — Reinforcement  for 
Column  Footing. 


480  SPREAD   FOUNDATIONS  CHAP.  XV 

and  ABKL  about  EF,  GH  and  KL  respectively;  in  other 
words,  it  will  be  assumed  that  there  is  no  stress  on  the  planes 
AD  and  BC.  Dividing  the  horizontal  distance  between  AB 
and  DC  into  four  equal  parts  by  the  lines  bi,  b2  and  63,  the  lengths 
of  the  lines  60,  &i,  &2,  63  and  54  are  respectively  8.50,  6.79,  5.08, 
3.37  and  1.67  ft.  Let  AI,  Az,  A3  and  A±  represent  respectively 
the  areas  of  the  base  of  the  footing  to  the  right  of  the 
b  lines  of  the  corresponding  subscripts,  then  their  values  will 
be^4i=  6.54,  ,42  =  ii. 6,  ^3  =  15.2  and  ^4  =  17.35,  all  expressed 
in  square  feet. 

The  upward  pressure  from  the  soil  is  2ioooo/(8.5)2=29io 
Ibs.  per  sq.  ft.  The  shears  on  the  sections  &i,  b2,  bs  and  &4  are 
respectively  19  ooo,  33  ooo,  44  200  and  50  500  pounds.  The 
moment  of  the  upward  pressure  to  the  right  of  and  about  bi 

is   19  oooX  2><8-5+6-79xoJ54  Xi2  =  ioiooo    Ib.-in.     The 

8.5+6-79  3 

moments  of  the  forces  to  the  right  of  and  about  b%,  bs  and  b± 
are  respectively  376000,  775000,  and  i  267000  Ib.-in.  Using 
an  allowable  unit  stress  for  the  rods  of  16  ooo  Ibs.  per  sq.  in. 
and  for  the  concrete  of  650  cos2  01  =  500  (approximately)  Ibs. 
per  sq.  in.,  in  which  a  is  the  angle  made  by  the  upper  surface 
with  the  horizontal,  the  values  of  d  as  given  in  the  [formula 
d  =  M/(Rb)  are  ^1  =  4. 2,  J2  =  9-3,  ^3  =  16.4  and  ^4=29.8  in. 

Using  the  formula  A=M/(fsjd)  to  get  the  required  area  of 
cross-section  of  steel  at  bi,  62,  £3  and  64,  the  respective  values 
are  1.69,  2.83,  3.30  and  2.97  sq.  in.  Assuming  12  square 
twisted  rods,  the  required  area  of  each  one  is  3.30/12  =  0.275 
sq.  in.  A  iVinch  rod  furnishes  an  area  of  0.316  sq.  in.  The 
rods  will  be  placed  as  shown  in  Fig.  1586,  each  layer  being 
ij  in.  above  the  one  below  it. 

The  ordinates  to  the  curved  line  in  Fig.  1586  represent  the 
required  depths,  but,  as  shown  in  the  same  illustration,  the 
depths  adopted  will  be  greater  than  these. 

The  bond  stresses  as  given  by  the  formula  u=(Sd  —  M  tan  a)/ 
o)  are  48,  50,  44  and  36  Ibs.  per  sq.  in.  for  the  sections 
bz,  bz,  and  b±  respectively. 

The  maximum  unit  shear  is  fc  tan  01  =  500X0.586  =  293  Ibs. 


ART.  159 


CONCRETE  SPREAD  FOUNDATIONS 


481 


per  sq.  in.  This  is  a  rather  high  value  but  as  it  occurs  at  the 
point  of  maximum  compression  and  so  does  not  develop  a 
heavy  diagonal  tension,  it  may  be  considered  safe. 

Assuming  that  the  concrete  takes  no  direct  tension  the 
maximum  diagonal  tension  for  each  section,  as  given  by  the 
formula  t=(Sd  —  M  tan  a)/(bjd2),  is  /i=i6,  £2  =  22,  £3  =  29  and 
/4  =  48  Ibs.  per  sq.  in.  Hence  stirrups  are  required  for 
only  a  short  distance  from  the  face  of  the  column.  The 
method  of  design  of  the  same  is  treated  in  Art.  157  and  will 
not  be  repeated  here. 

The  design  of  the  slab-and-beam  type  of  footing  follows 
closely  the  method  of  design  of  slabs  and  beams  in  building 
construction.  The  slab  serves  as  a  beam  to  carry  the  load 
from  the  soil  to  the  beam,  the  span  being  taken  as  the  distance 
center  to  center  of  beams;  and  the  latter,  acting  as  cantilevers, 
carry  it  to  the  column.  Where  the  beams  have  constant  cross- 
sections  the  formulas  for  stresses  as  derived  in  any  standard 
treatise  on  reinforced  concrete  are  applicable,  and  where 
tapered,  the  formulas  given  in  Art.  157  may  be  used.' 

Where  one  footing  serves  for  two  columns,  the  method  of 
obtaining  the  shape  of  footing,  as  well  as  the  shears  and  bending 
moments,  is  similar  to  that  for  the  I-beam  grillage  (Art.  154), 
while  the  standard  formulas  are  applicable  in  finding  the  stresses. 
On  page  647  of  the  second  edition  of  TAYLOR  and  THOMPSON'S 
Concrete,  Plain  and  Reinforced,  an  example  of  this  type  of  foot- 
ing is  worked  out. 


ART.  159.     CONCRETE  SPREAD  FOUNDATIONS 

Two  standard  forms  of  the  reinforced-concrete  spread  foot- 
ings used  for  the  column  foundations  of  a  railway  terminal  sta- 
tion at  Atlanta,  Ga.,  are  shown  in  Fig.  1590.  The  one  illus- 
trated on  the  left  was  used  for  20  X  24-inch  columns  and  was 
in  the  form  of  a  truncated  pyramidal  slab  reinforced  with 
bars  and  stirrups.  The  one  shown  on  the  right  was  of  the 
beam-and-slab  type.  The  details  are  sufficiently  shown  to 
require  no  explanation. 
31 


482 


SPREAD   FOUNDATIONS 


CHAP.  XV 


The  125-foot  concrete  block  chimney  for  the  St.  Joseph's 
Home,  Chicago,  was  founded  on  a  blue  clay,  the  base  of  the 
foundation  extending  about  5  feet  below  the  surface  of  the 
ground.  The  footing,  shown  in  Figs.  159^  and  c,  consists 
of  a  circular  slab  24  feet  in  diameter  and  10  inches  thick,  on 
which  is  built  a  box  with  a  square  outer  surface  8  feet  3  inches 
on  a  side,  and  with  an  octagonal  inner  surface  about  6  feet  7 


{"Diagonal 
Rod 


^'Diagonal 
Rod 


FIG.   1590. — Pyramidal  and  Ribbed  Slab  Footings  of  Reinforced  Concrete,  Atlanta 
Terminal  Station,  Southern  Railway. 

inches  between  opposite  faces.  The  box  is  about  4  feet  high. 
laFrom  either  corner  of  this  box  extends  a  series  of  eight 
cantilever  ribs  reaching  approximately  to  the  outer  edge  of  the 
slab  as  shown  in  the  accompanying  view.  These  cantilever 
ribs  are  each  14  inches  wide,  4  feet  deep  at  the  box  and  slope 
off  uniformly  to  a  width  of  8  inches  at  the  top  of  the  slab. 


Engineering  Record,  vol.  65,  page  636,  June  8,  1912. 


ART.  159 


CONCRETE  SPREAD  FOUNDATIONS 


483 


Round  Bars          {/"Round  Ba 


|« 


FIG.   1596. — Slab  and  Box  Footing  of  Reinforced  Concrete  for  a  1 25-foot  Chimney 

in  Chicago. 


FIG.   i59c. View  of  the  same  Footing  as  shown  in  Fig.  1596. 


484 


SPREAD    FOUNDATIONS 


CHAP.  XV 


Their  effective  depth  is  virtually  4  feet  plus  the  effective  depth 
of  the  slab,  as  they  are  built  integral  with  it;  and  their  rein- 
forcement, which  consists  of  i-inch  round  bars  and  J-inch  ver- 
tical stirrups,  extends  up  from  the  lower  surface  of  the  slab,  as 
shown  in  the  accompanying  drawing.  The  base  is  thus  made 
up  of  a  series  of  slabs,  each  supported  by  the  adjacent  canti- 
lever ribs  and  reinforced 
with  f-inch  round  bars 
spaced  according  to  the 
position  of  the  slab  in  the 
base.  That  portion  of 
the  base  enclosed  at  the 
center  is  reinforced  with 
a  double  system  of  J-inch 
round  bars,  spaced  6j 
inches  on  centers." 

Fig.  159^  illustrates  a 
reinf  orced-concrete  footing 
on  a  pile  foundation,  Fig. 
1590  represents  a  novel 
type  of  foundation  used 
for  a  loft  building  in  New 
York  City.  There  were 
three  lines  of  columns,  two 
lines  of  wall  columns  and 
one  line  through  the  cen- 
.io'-8- — —****+*  ter.  The  foundation  pre- 


tf'Bar  Rmqs 
s  Welded  J 


\ 

V    .'Fastened 

X- 

1 

/,  '^""Rmq.Welded        $' 

4 

n-~n                             r~ 

feas  ! 
i   i^  r 

*LLU 

LLU           L 

UJ  ' 

FIG.  159^. — Column  Footing  of  Reinforced 
Concrete  Supported  by  Pre-molded  Concrete 
Piles. 


sented  something  of  a 
problem  because  the  ad- 
joining structure  rested 

on  a  pile  foundation,  which  the  architect  feared  was  in  a  poor 
condition.  On  account  of  the  desire  not  to  be  forced  to  the 
expense  of  underpinning  this  adjoining  building,  a  deep  founda- 
tion was  out  of  the  question.  The  simple  spread  footing  could 
not  be  used  for  the  wall  columns  because  of  lack  of  space.  As 
finally  constructed,  the  foundation  consisted  of  a  solid  frame- 
work of  reinforced-concrete  beams. 


ART.  159 


CONCRETE  SPREAD  FOUNDATIONS 


485 


1  "The  special  feature  of  the  cantilever  construction  is  that 
the  one  cross-beam  and  a  portion  of  each  longitudinal  beam 
form  a  T-section,  the  center  of  gravity  of  which  is  the  same 
as  the  center  of  gravity  of  the  column  loads  plus  the  weight  of 
the  side  wall.  Thus,  looking  at  Fig.  1590,  it  will  be  seen  that 
half  of  the  load  coming  on  the  column  in  the  center  of  the  build- 
ing and  the  whole  load  coming  on  a  wall  column  and  the  wall 


- 10-7*— >k-5-8*>K -K>'-9"^5L8"^  B    j    * 

'-5* >!<: 74-5*— >k M--5" >    ^ 


k- -  /4-5-*-~- 

EN&.NEWS 


FIG. 


; — pian   of   Reinforced-Concrete    cantilever    Footings   of    1 2-story   Loft 
Building,  25-29  West  3ist  Street,  New  York  City. 


load  adjacent  to  that  column  is  carried  on  that  portion  of  the 
side  concrete  beam  and  the  cross-beam  there  shown,  and  that 
the  center  of  gravity  of  these  loads  is  the  same  as  the  center 
of  gravity  of  the  T-beam  formed  by  the  side  beam  with  the 
transverse  beam  going  at  right  angles  from  it.  The  .variation 
in  the  loads  and,  consequently,  in  the  centers  of  gravity,  re- 
sulted in  different  shapes  and  sizes  of  the  supporting  beams." 

1  Engineering  News,  vol.  68,  page  995,  Nov.  28,  1912. 


486 


SPREAD   FOUNDATIONS 


CHAP.  XV 


Reinforced-concrete  spread  foundations  covering  the  whole 
area  of  the  basement  were  used  for  the  factories  of  Herman 
Behrf&  Co.,  and  W.  H.  Sweeney  Mfg.  Co.,  Brooklyn,  N.  Y. 
Fig.  I59/  shows  the  details  for  the  first-named  factory.  This 
raft  foundation,  which  was  of  the  beam-and-slab  type,  had  a  slab 
thickness  of  i  foot  and  a  beam  thickness  of  3" feet.  The  beams 
formed  continuous  lines  under  the  outer  wall  and  along  the  cen- 
ter line  of  the  columns  lengthwise  of  the  building,  the  column  spac- 
ing being  16  feet  10  inches  longitudinally  and  approximately 
79!  feet  transversely.  These  beams  were  5  feet  wide  under  the 


sS-lM'Sq.  Straight  Bars 

f '_£. !  ^Boxment  Floor       ^ 

£. .—.—.—.  J-'.-.-i-.-j  'ft — , 


-l"5q.BarJ, 
/7'3"hng. 

^•:^^^6'c-K>c- 


Center  Line* 


f  - 


'   uT-L    •     f    t~ l~!"t  •  •  r -jTl" [it '-i  T  . 

ffll-^^^^Rrj-tttl-^^ 

FIG.   iS9/. — Spread  Foundation. 


FIG.   i59g. — Spread  Foundation. 


walls  and  6  feet  wide  under  the  columns.  The  intervening 
space  between  beams  was  brought  up  nearly  to  surface  level 
by  a  dirt  fill,  and  a  finished  concrete  floor  was  laid  over  the 
whole  area.  As  shown  in  the  illustration  the  reinforcement  for 
the  1 2 -inch  slab  consisted  of  transverse  bars  i  inch  square, 
spaced  5  inches  on  centers  and  3  inches  from  the  top  of  the  slab. 
The  beams  under  the  columns  were  reinforced  with  eleven 
i  J-inch  square  bars  near  the  upper  surface,  the  five  center  bars 
being  carried  through  straight  and  the  six  outside  bars  bent 
down  under  the  column. 

The  foundation  of  the  W.  H.  Sweeney  Mfg.  Company's 
factory  consisted  of  a  slab  over  the  whole  area  surmounted  by 
truncated  pyramidal  slabs  under  all  the  columns  and  a  trape- 


ART.  159  CONCRETE   SPREAD   FOUNDATIONS 

•ss 


487 


Wariest 


Section  A- B. 


Section  Section   E-F. 

C-D. 


Section  6~H. 
(Detail  of  Footing) 


FIG.  i59/*. — Reinforced- concrete  Arch  Foun- 
dation    of   Warehouse    at   418-426  West 
Street,   New  York  City. 


488 


SPREAD   FOUNDATIONS 


CHAP.  XV 


zoidal-shaped  slab  under  the  wall,  as  shown  in  Fig.  159^.  The 
columns  were  spaced  approximately  16  feet  on  centers  in  both 
directions.  The  column  footings  were  raised  2  feet  6  inches 
above  the  top  of  the  raft  slab  and  the  latter  was  reinforced 
with  six  lines  of  rods  about  i^  feet  on  centers,  and  laid  in  both 
directions  along  the  center  lines  of  the  columns.  Further  rein- 
forcement was  used  in  the  bottom  of  the  slab  under  the  columns 
and  walls,  as  shown  in  the  illustration. 

The  inverted  arch  foundation  of  reinforced  concrete  as  used 
for  a  building  in  New  York  City  presents  an  unusual  type  of 
spread  foundation.  Its  adoption  was  due  to  the  necessity  of 
having  a  very  shallow  foundation.  The  limit  of  depth  fixed 


— >K td'O'. 

.rmi— ,  ~ 


Col.3    Sub  Basement  Floor 

^hSLm 


.  ........  J«.  .................  2&0/  --------  -  .........  4« 

Co/p  Fin  SubBosement  Floor    CoAg 


^-Waterproofing 
SECTION  Y-Y 

'• ~ >!< 26^ -J 

Cokl4 


s 


Wate'-proofinoj 


FIG.   159*. — Cellar  Floor  Sections  Showing  Grillage  Beams  and  Reinforced-Concrete 
Girders,    Pope    Building,    Cleveland,    O. 

by  the  architect  was  not  sufficient  for  isolated  reinforced-con- 
crete  footings,  and  as  steel  I-beam  grillages  would  have 
cost  about  25  percent  more,  the  inverted  arch  form  was 
used.  The  arches  ran  in  both  directions  between  columns  as 
shown  in  Fig.  159^.  They  were  12  inches  deep  at  the  crown 
and  42  inches  deep  under  the  cast-iron  column  bases,  and  varied 
from  4  to  5  feet  in  width.  The  reinforcement  consisted  of  |- 
inch  round,  straight,  corrugated  bars  in  the  bottom,  spaced 
6  inches  on  centers,  and  i|-inch  bent  bars  in  the  top,  spaced 
the  same  distance.  All  end  spans  were  made  of  rectangular 
or  T-shaped  concrete  beams,  to  provide  for  the  thrust  in  the 
adjoining  arches.  For  further  details  see  Engineering  News, 
vol.  66,  page  763,  Dec.  28,  1911. 

In  the  foundation  for  the  Pope  Building,  Cleveland,  Ohio,  a 


ART.  159 


CONCRETE  SPREAD  FOUNDATIONS 


489 


combination  of  a  steel  grillage  and  a  reinforced-concrete  raft 
foundation  was  used.  The  material  upon  which  the  founda- 
tion was  placed  consisted  of  a  few  feet  of  quicksand  overlying 
clay.  As  the  sides  of  the  lot  were  enclosed  by  a  permanent 
steel  cofferdam  extending  well  down  into  the  clay,  the  quick- 
sand was  not  subject  to  outside  disturbance,  and  hence  made  a 
satisfactory  cushion.  A  6-inch  layer  of  concrete  was  first 
spread  over  the  bottom  and  covered  with  tar  and  felt  water- 
proofing, after  which  a  1 6-inch  layer  of  concrete  was  placed 
on  the  waterproofing.  On  this  were  located  the  I-beam  gril- 
lages, as  shown  in  Fig.  1592',  section  A- A  being  taken  at  right 
angles  to  the  street  and  section  Y-Y  parallel  with  the  street. 
The  grillages  were  made  of  two  tiers  of  24-inch  I-beams,  each 
supporting  a  single  column.  In  all  the  intermediate  spaces 
the  concrete  floor  slab  was  reinforced  with  rods,  thus  providing 
for  the  distribution  of  the  column  loads  over  the  entire  bottom. 


CHAPTER  XVI 
UNDERPINNING  BUILDINGS 

ART.  1 60.     NEEDLE-BEAM  UNDERPINNING 

The  technical  term  underpinning  is  used  to  denote  the  placing 
of  new  foundations  or  supports  under  existing  structures.  As 
an  engineering  art  and  science  this  work  has  been  developed 
almost  entirely  in  a  few  large  cities,  notably  New  York,  Chicago 
and  Boston.  In  New  York  the  subways  and  the  modern 
'sky-scraper,'  with  its  foundations  carried  far  below  those  of 
surrounding  structures,  have  compelled  the  placing  of  new  and 
deeper  foundations  for  many  buildings.  Some  of  these  under- 
pinned buildings  have  wall  loads  as  high  as  45  tons  per  linear 
foot  and  column  loads  of  300  tons  or  more.  The  underpinning 
of  such  heavy  buildings  requires  great  skill  and  care,  for  it  must 
be  done  in  such  a  manner  that  no  settlement  occurs;  with 
the  mechanical  equipment  of  the  modern  office  building,  such 
as  elevators,  motors,  engines,  etc.,  a  very  slight  differentia) 
settlement  often  causes  trouble.  Moreover,  the  work  must 
often  be  done  hastily  and  in  a  limited  space. 

The  two  general  methods  of  underpinning  are :  First,  the  use 
of  needle-beams  to  support  the  structure  temporarily,  after 
which  the  old  foundations  are  removed  and  new  ones  placed; 
and  second,  the  use  of  vertical  cylinders  (without  temporarily 
supporting  the  structure)  in  the  plane  of  and  under  the  walls, 
carried  down  to  solid  bearing. 

The  needle-beam  method  of  underpinning  may  be  called 
the  indirect  method  since  the  function  of  the  needle-beams  is 
merely  to  take  the  loads  temporarily  from  the  old  foundation 
to  permit  removing  the  latter  and  the  building  of  new  founda- 
tions. This  method  is  the  older  and  more  widely  used,  being 
universally  applied  where  the  new  foundation  is  of  a  simple 
type  and  not  carried  to  a  great  depth. 

490 


ART.  1 60 


NEEDLE-BEAM   UNDERPINNING 


49 1 


The  fundamental  principle  of  the  needle-beam  method  con- 
sists in  cutting  holes  through  the  walls  of  the  building  at  inter- 
vals of  from  3  to  10  feet  or  more,  depending  somewhat  on  the 
strength  of  the  walls,  and  placing  wooden  or  steel  beams  through 
these  openings.  The  ends  of  the  beams  are  held  on  temporary 


J  ^      k 


W^-^:V^-  "W-W--W-:! 


UUiJ 


FIG.   i6oa. — First  Step. 


FIG.   1606. — Second  Step. 


supports  placed  at  a  sufficient  distance  from  the  wall  to  permit 
excavation  and  reconstruction  work  to  be  carried  on  under  the 
wall.  The  needles  are  raised  by  placing  jacks  under  the  ends 
of  the  beams  until  they  take  bearing  on  the  wall  and  thus  lift 
the  latter  from  its  old  foundation. 


FIG.   i6oc.— Third  Step. 


FIG.   i6od. — Fourth  Step. 


Figs.  i6oa-d  illustrates  the  general  method  used  in  under- 
pinning the  Cross  Building,  New  York  City.  1  "The  first  step 
was  to  cut  through  the  old  brick  wall,  which  was  56  inches  thick, 

Engineering  News,  vol.  68,  page  1134,  Dec.  19,  1912. 


49  2        .  UNDERPINNING  BUILDINGS  CHAP.  XVI 

an  opening  large  enough  to  allow  the  entering  of  the  needle- 
beams,  made  up  of  four  24-inch  I-beams.  .  .  .  The  needles, 
which  were  spaced  about  6  feet  apart  along  the  wall,  were 
supported  on  the  inside  of  the  old  building  by  blocks  placed  on 
the  concrete  cellar  floor,  and  on  the  outside  by  blocks  supported 
on  the  earth  immediately  alongside  the  wall.  Sheathing  was 
then  driven  outside  of  the  blocks,  and  an  excavation  made  to 
solid  rock.  On  this  rock  a  rough  concrete  footing  was  placed 
and  12X1 2-inch  posts  erected  to  carry  the  outside  end  of  the 
needle-beams,  the  needle-beams  then  being  supported  on  the 
inside  by  blocking  on  the  concrete  pavement  and  on  the  out- 
side by  heavy  posts  on  a  solid  concrete  footing.  Shims  were 
driven  in  under  the  brick  wall  for  support  and  sheathing 
driven  on  the  inside  of  the  old  building,  as  shown  in  Fig. 
i6oc.  Excavation  was  then  made  under  the  brick  walls  to 
rock  bottom,  and  the  entire  old  footing  removed.  A  new  con- 
crete footing  was  placed  on  this  rock  bottom."  .  .  . 

Oftentimes  conditions  make  it  impossible  to  occupy  the  space 
on  both  sides  of  the  wall,  the  space  on  the  inside  being  perhaps 
occupied  by  a  store  or  storage  room;  or  the  space  on  the  out- 
side is  taken  up  with  other  construction  work.  In  either  case 
the  method  just  described  must  be  modified.  One  way  of 
avoiding  interior  work  is  to  use  the  figure-4  needle-beam  as 
described  in  Art.  164.  A  number  of  arrangements  may  be  em- 
ployed to  avoid  occupying  space  outside  the  wall,  among  which 
the  most  widely  used  is  the  cantilever  needling  plan  described 
in  Art.  163;  another  scheme  uses  needle-beams  of  the  regular 
type  at  considerable  distances  apart,  the  intermediate  needles 
having  their  outside  ends  bearing  on  a  truss  or  girder,  parallel 
and  close  to  the  wall  on  the  outside,  the  ends  of  the  truss  or 
girder  bearing  on  the  regular  needles.  This  method  materially 
reduces  the  space  used  on  the  outside. 

DESIGN  OF  NEEDLE-BEAMS. — Probably  the  most  difficult 
feature  in  the  design  of  a  needle-beam  system  lies  in  estimating 
the  load  on  any  particular  member.  The  rest  of  the  design  is 
a  matter  of  elementary  mechanics  and  needs  no  discussion  here. 
The  total  weight  of  the  structure  to  be  supported  can  usually 


ART.  161 


EXAMPLES   WITH  NEEDLE-BEAMS 


493 


be  approximated  with  sufficient  accuracy;  if  the  needle-beams 
are  spaced  at  equal  distances  apart,  it  will  ordinarily  be  assumed 
that  all  take  the  same  load.  To  make  this  a  fact,  care  should 
be  exercised  to  have  all  jackscrews  raised  the  same  amount. 
A  good  scheme  is  to  have  one  or  two  men  do  all  this  work,  giv- 
ing each  jackscrew  perhaps  half  a  turn  at  a  time. 


ART.  161.     EXAMPLES  WITH  NEEDLE -BEAMS 

Needle-beams  are  usually  supported  in  one  of  the  following 
ways:  First,  by  struts  resting  on  concrete  bases;  second,  on 
piles;  or  third,  on  cribbing  built  on  the  surface  of  the  ground. 
The  first  method  is  satisfactory  where  the  loads  are  not  unduly 
large  and  where  good  bearing  can  be  obtained;  it  also  takes 
up  the  least  space.  Where  the  ground  is  soft  a  pile  foundation 


Bearin 


2Afi  IOO*30'o'Long 


Present  WoilFy/ 


-:^:;---v"^-r^WV 

We? 

New  Wall- 


FIG.   i6ia. — Underpinning  with  Needle  Beams  and  Pile  Bents. 

is  the  only  satisfactory  method  of  insuring  absolute  stability. 
The  crib  form  may  be  used  where  the  loads  are  large  and  must 
be  distributed  over  a  considerable  area  of  the  ground.  Fig. 
i6od  illustrates  the  strut  method  of  support,  the  details  of 
which  are  described  in  Art.  160. 

Fig.  i6ia  shows  the  details  of  the  method  used  for  under- 
pinning buildings  adjacent  to  the  Adams  Express  Building, 
New  York  City.  Here  the  inside  ends  of  the  needles  were 
supported  on  blocking  resting  on  the  cellar  floor,  while  the 


494 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


outside  ends  rested  on  12X1 2-inch  timbers  running  parallel 
to  the  wall,  under  which  were  the  5o-ton  jacks  used  in  raising 
and  supporting  the  wall.  These  in  turn  rested  on  small 
blocks  which  took  bearing  on  longitudinal  12X1 2-inch  timbers, 
the  latter  resting  on  pile  bents. 


•J-e'St-eo/  Pipes 


FIG.   i6ib. — Underpinning  a  3oo-ton   Column  on   Quicksand,    Sargent    Building, 

New  York  City. 

Fig.  i6ib  illustrates  the  form  of  needling  which  uses  only 
cribwork  for  its  support.  The  needle-beams,  of  which  there 
are  four,  support  a  300- ton  column.  luThe  first-floor  beams 
were  blocked  and  wedged  up  on  the  girders  close  to  the  columns, 

1  Engineering  Record,  vol.  61,  page  649,  May  14,  1910. 


ART.  162 


SUPPORTING   WALL  BELOW  BEAMS 


495 


and  sills  were  laid  across  them  on  the  first  floor  adjacent  to 
the  column  to  receive  two  pairs  of  posts  wedged  to  bearing  on 
the  under  side  of  the  box  girder  close  to  the  column.  The 
wedges  were  driven  and  the  jacks  operated  to  take  the  floor 
and  wall  loads  from  the  column  to  the  cribbing  and  to  compen- 
sate for  any  settlement  of  the  latter." 

Fig.  1620  shows  the  method  of  underpinning  the  Benedict 
Building,  New  York  City.  The  needle-beams  rested  on  struts 
on  the  outside  and  cribbing  on  the  inside.  Holes  about  5 
feet  apart  were  first  cut  in  the  wall  and  into  these  holes  were 
inserted  needle-beams  composed  of  1 5-inch  I-beams  in  groups 
of  three,  each  group  being  tied  together  with  iron  yokes  at  both 
ends.  On  the  outer  end  of  the  needle-beams  two  2o-ton  jack- 
screws  rested  on  two  i2Xi2-inch  vertical  posts  and  took 
bearing  against  horizontal  steel  plates  on  the  lower  flanges 
of  the  I-beams.  The  posts  took  bearing  at  their  lower  ends 
on  5 X 5-foot  grillages  of  i2Xi2-inch  timbers  resting  on  the 
concrete  footing. 


ART.  162.     SUPPORTING  WALL  BELOW  BEAMS 

With  the  needle-beam  method  of  underpinning  it  is  usually 
impracticable  to  support  the  wall  from  below  the  old  founda- 
tion. For  this  reason,  if  the  new  foundation  is  to  be  con- 
structed only  up  to  the  old,  it  becomes  necessary  to  use  some 
special  method  of  supporting  the  wall  and  old  foundation 
below  the  needling. 

In  the  case  of  the  Benedict  Building,  Fig.  1620,  this  was 
done  as  follows:  1 " Narrow  excavations  were  made  between  the 
old  wall  and  the  sheeted  pits,  and  the  latter  were  braced  against 
the  face  of  the  masonry  as  the  excavation  proceeded.  When  it 
reached  the  bottom  of  the  old  footing,  small  drifts  were  extended 
under  it  and  in  them  'springing  needles',  each  consisting  of 
a  pair  of  i2Xi2-inch  horizontal  timbers  bolted  to  the  verti- 
cal shores,  were  inserted  with  their  ends  bearing  against  the 
bottom  of  the  old  footing.  Vertical  chains  with  turnbuckle 

'Engineering  Record,  vol.  55,  page  267,  March  2,  1907. 


496 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


adjustments  were  attached  to  the  I-beam  needles  above,  close 
to  the  face  of  the  wall,  and  engaged  the  springing  needles, 
formed  fulcrums  for  the  latter  which  acted  as  cantilevers  sup- 
porting the  footing  below  the  main  needle-beams.  A  vertical 


CITY  INVESTING  CO.  BUILDING 


BENEDICT  BUILDING 


FIG.   1620. — Underpinning  Methods  for   Benedict   Building,   New  York. 

strut  was  inserted  between  the  ends  of  the  springing  beams 
and  the  I-beam  needles  to  relieve  the  connection  to  the  vertical 
shores  and  take  the  upward  cantilever  reaction." 

Fig.  1626  illustrates  another  method  for  a  suspended  sup- 


ART.  163 


THE    CANTILEVER   METHOD 


497 


port  for  the  footing.  l "  A  steel  bearing  plate  was  seated  across 
the  top  flanges  of  each  pair  of  I-beams  and  gave  bearing  for 
the  nuts  on  the  upper  ends  of  two  2-inch  vertical  rods  about 
7  feet  long.  The  nuts  on  the  lower  ends  of  these  rods  engaged 
a  cross  plate  or  saddle,  forming  a  fulcrum  for  an  8-inch  hori- 
zontal cantilever  I-beam  10  feet  long.  The  long  arms  of  the 
cantilever  reacted  upward  against  some  of  the  I-beam  stringers 
supporting  the  outer  ends  of  the  needle-beams.  The  short 


FIG.   1626. — -Suspended  Support  for  Footing,  Silversmith' s  Building,   New  York. 

arms  took  bearings  about  2  feet  long  on  the  under  side  of  the 
old  concrete  footing,  supporting  it  across  the  thickness  of  the 
wall,  so  that  when  undermined  by  the  excavation  for  the  new 
foundation  the  old  footing  looked  in  cross-sections  like  a 
cantilever  projecting  about  2  feet  beyond  the  inner  face  of  the 
wall  and  proved  strong  enough  to  resist  the  bending  moment 
thus  developed. " 

ART.  163.     THE  CANTILEVER  METHOD 

Where,  for  some  reason,  the  work  cannot  be  carried  on  from 
both  sides  of  the  wall,  the  cantilever  method  may  be  employed. 
The  possible  modifications  of  this  method  are  many,  but  two 
examples  are  illustrated  to  show  the  fundamental  principles. 
In  the  construction  of  the  present  building  at  No.  42  Broad- 

1  Engineering  Record,  vol.  56,  page  348,  Sept.  28,  1907. 
32 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


way,  New  York  City,  it  was  necessary  to  sink  caissons  close 
to  the  seven-story  building  then  occupying  the  site  of  No.  44 
Broadway.  In  order  not  to  delay  the  sinking  of  the  caissons 
it  became  necessary  to  avoid  supporting  some  of  the  needle- 
beams  on  the  site  of  No.  42.  For  this  reason  the  scheme  shown 
in  Fig.  1 63 a  was  adopted. 

luTwo  groups  of  five  20-inch  I-beams,  30  feet  long  and  21 
feet  apart  in  the  clear,  were  put  through  the  foot  of  the  wall 


Crib. 


Fulcrum  Beams  suspended 
from  Needle  Girders 


FIG.   163(1. — Counter- weighted    Needle   Beams  and  Girders,   for   Building  at   44 
Brtfadway,  New  York  City. 


at  right  angles  and  supported  on  crib  work  and  jackscrews 
at  both  ends.  In  building  No.  44  there  were  suspended  from 
both  groups  close  to  the  wall,  four  24-inch  I-beams  30  feet 
long  carried  on  yokes  screwed  up  close  to  the  under  side  of 
the  needle  girders.  These  beams  served  as  a  fulcrum  to  sup- 
port three  sets  of  four  20-inch  cantilever  I-beams  each.  These 

Engineering  Record,  vol.  48,  page  698,  Dec.  5,  1903. 


ART.  163 


THE   CANTILEVER  METHOD 


499 


Pig  Iror 
Brick  Pier- 
Recess 


ii       il        \  Section  Y-Y  ji  I*PM  KK*  ; 

^^BL^^  i     ^^>^><^^r    i  *^'"f 

///////      '//// //Y 

T^M 


ax 

7/7 


Sectional  Elevation  X'X 


K--  -^  - About  10' 0" 

h/4^/ 


JLtafcLMLU 


Secnonal  Elevat,on  V-V  Secfl°n  W'W 

FIG.    1636. — Arrangement  of  Underpinning,  92-94  Maiden  Lane,  New  York  City. 


5OO  UNDERPINNING  BUILDINGS  CHAP.  XVI 

cantilevers  were  located  in  the  center  and  at  both  ends  of  the 
section  of  the  wall  included  between  the  needle  girders  so  as  to 
leave  about  equal  space  between  them.  They  converged  in  No. 
44  where  a  platform  was  built  on  their  extremities  and  loaded 
with  pig  iron  to  form  a  counterweight  against  the  upward 
reaction.  The  wall  was  supported  on  the  needle  girders  and  on 
the  ends  of  the  cantilevers  by  double  rows  of  special  20- ton 
jackscrews." 

An  example  of  underpinning  in  which  all  the  supporting 
was  done  from  the  inside,  in  order  not  to  interfere  with  con- 
struction work  carried  on  outside,  is  shown  in  Fig.  163  b.  The 
needle-beams,  with  their  ends  inserted  in  holes  in  the  wall, 
were  fulcrumed  on  jackscrews  5  feet  from  the  inside  face  of 
the  wall.  The  beams  took  bearing  on  blocks  of  wood  which 
were  bored  at  each  end  for  a  4-inch  jackscrew  and  which  rested 
on  cast-steel  nuts  engaging  the  screws.  The  lower  ends  of  the 
screws  took  bearing  on  cast-steel  base  plates  seated  on  sills 
which  transmitted  the  load  to  a  timber  grillage.  Auxiliary 
supports  were  wedged  up  against  the  needles  to  take  the  load 
in  case  of  failure  of  the  jacks. 

The  wall  loads  were  transferred  to  the  needles  through 
timber  blocks  with  a  few  inches  of  cement  on  top  to  develop 
more  uniform  bearing.  The  sets  of  needles  were  spaced  9  or 
10  feet  apart,  but,  as  shown  in  Section  W-W,  Fig.  163^,  inter- 
mediate bearing  was  obtained  through  blocking  and  wedges 
resting  on  an  8  X  8-inch  horizontal  beam.  Supporting  tim- 
bers were  jacked  up  under  the  lower  flanges  of  the  needles  in  the 
plane  of  the  wall  as  a  precautionary  measure,  until  the  new 
foundation  was  ready  to  be  constructed. 

The  long  arms  of  the  cantilevers  reacted  against  the  main 
floor  girders  in  the  first  floor  through  blocking  and  wedges, 
and  were  further  held  down  by  cast-iron  ballast  and  by  anchor- 
ing to  the  piers  through  pairs  of  horizontal  I-beams.  The 
latter  engaged  recesses  in  the  piers  and  had  transverse  pieces 
across  their  bottom  flanges.  To  these  transverse  pieces  were 
attached  lengths  of  wire  rope  passing  up  over  the  blocks  on 
top  of  the  needles. 


ART.  164  FIGURE-FOUR   NEEDLES  501 

ART.  164.     FIGURE-FOUR  NEEDLES 

The  methods  explained  in  the  last  article  are  used  where  it  is 
necessary  to  avoid  using  space  on  the  outside  of  the  building. 
Where  there  is  no  available  space  on  the  inside,  the  figure-4 
method  is  generally  employed. 

Fig.  1640  shows  the  details  of  this  method  as  used  in  the  Bene- 
dict Building,  New  York  City.  Pits  5  feet  square  and  about  6 
feet  on  centers  were  first  excavated  and  sheeted  to  about  30  feet 
below  the  curb,  and  on  the  bottom  a  3-foot  layer  of  concrete  was 
placed.  On  this  concrete  a  timber  grillage  was  erected  to  dis- 
tribute the  load  from  a  i2Xi2-inch  shore  to  the  concrete  foot- 
ing. The  lower  ends  of  the  shores,  which  were  about  30  feet 
long,  took  bearing  against  short  horizontal  timbers,  the  latter 
in  turn  bearing  against  either  one  or  two  jackscrews  reacting 
against  foot  blocks.  The  upper  end  of  each  shore  was  sur- 
mounted with  a  saddle  plate  and  wedges  and  was  notched  into 
the  wall.  The  saddle  plate  gave  bearing  to  i-inch  vertical  rod 
suspenders,  to  the  lower  ends  of  which  were  fastened  turnbuckles 
and  chains,  engaging  the  12X1 2-inch  needle-beams. 

The  springing  needles,  which  by  a  cantilever  action  took  the 
load  from  the  wall,  were  placed  by  first  excavating  the  space 
between  the  sheeted  pits  and  the  wall.  The  outer  ends  were 
bolted  to  the  inclined  shores  and  took  bearing  against  reaction 
cleats  above  them. 

To  take  the  weight  of  the  wall  from  the  old  footing  the  jack- 
screws  were  first  operated  to  bring  the  shore  to  a  tight  bearing 
to  take  some  of  the  weight  of  the  wall  above,  after  which  the 
turnbuckles  were  screwed  up  until  the  remainder  of  the  weight 
of  the  wall  was  transferred  to  the  system  of  needles. 

With  this  type  of  underpinning  a  very  stable  footing  must  be 
provided  for  the  lower  end  of  the  shore,  for,  whereas  with  the 
ordinary  form  of  needle  underpinning  a  part  of  the  weight  of 
the  wall  is  transferred  to  one  side  and  a  part  to  the  other,  here 
the  entire  weight  is  carried  to  one  side.  Another  condition  to 
guard  against  is  the  tendency  of  the  shore  to  push  in  the  wall  on 
account  of  the  horizontal  component  of  its  thrust^  This  hori- 


502 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


CITY  INVESTING  CO.  BUILDING 


Wed 
Saddle  plat 


BENEDICT  BUILDING 


FIG.   1640 — Underpinning  with  Figure-Four  Needle  Method,   Benedict  Building, 

New  York  City. 


FIG.   1646. — Use  of  Long  Shores   in  Underpinning  Cross   Building,    New  York. 

(Facing  p.  502.) 


ART.  165 


PLACING  THE  NEW  FOUNDATION 


503 


zontal  force  is  ordinarily  not  large  and  almost  any  building  has 
sufficient  strength  to  withstand  it  if  the  shore  be  inserted  at  a 
floor  level,  thus  permitting  the  floor  system  to  transmit  it  to  all 
parts  of  the  building. 

SHORES  OR  PUSHERS. — As  an  auxiliary  to  other  methods 
shores  are  often  used  in  underpinning  work.  Fundamentally 
they  are  the  figure  4  needle-beams  without  the  vertical  rod 


FIG.   164(7. — Showing  Ashlar  Face  Wall  of  the  Fanner's  Loan  &  Trust  Company's 
Building  in  New  York  City. 

and  horizontal  needles,  and  as  a  result  they  can  take  only  the 
weight  of  the  wall  above  the  points  at  which  the  struts  are 
notched  into  them.  For  this  reason  the  use  of  shores  must  be 
combined  with  some  other  type  of  underpinning.  Fig.  164^ 
shows  several  long  shores  inserted,  while  Fig.  164^  illustrates 
the  use  of  shorter  shores. 


ART.  165.     PLACING  THE  NEW  FOUNDATION 

As  the  object  of  underpinning  is  the  protection  of  foundations 
from  being  undermined  through  the  excavation  of  adjacent 


504 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


material  at  a  lower  level,  it  follows  that  in  general  only  those 
structures  having  shallow  foundations  will  require  underpinning. 
The  two  types  of  new  foundations  are  the  shallow  and  the  deep 
foundations.  The  former  consists  of  a  simple  masonry  or  con- 
crete footing,  or  of  a  spread  footing,  and  is  the  type  which  uses 
the  needle-beam  method  of  underpinning.  The  new  foundation 
is  placed  as  deep  as  the  new  excavation  is  to  be  made.  The  deep 
foundation  includes  the  cylinder,  the  caisson  and  the  tubular 
pile  piers.  Masonry  and  concrete  footings,  as  well  as  spread 
footings,  are  described  in  Chap.  XV. 


Curb  Level  El.  -t-is-i. 


CELLAR 
Ce/lar  Floor  El +6^} 


-Brick  Pier* 


Brick 
Restored 


Curb  LeveH 


VAULT 
Cel/ar Floor-? 


FIG.   i65<2. — Method  of  Underpinning  Centre  Street  Buildings,  New  York,  due  to 
Subway  Excavations. 

Where  pier  systems  are  used,  it  is  customary  to  give  the  wall 
no  temporary  support  as  the  sinking  operations  deprive  the 
wall  of  but  a  small  section  of  bearing  at  a  time.  Conditions 
sometimes  are  such  that  it  is  advisable  to  temporarily  sup- 
port the  wall  on  needle-beams  before  sinking  the  piers.  Such 
is  the  case  where  the  wall  is  weak  or  is  too  light  to  take  the 
cylinder  reactions. 

Fig.   1650  illustrates  a  case  in  which  steel  cylinders  were  use:l. 


ART.  165 


PLACING  THE   NEW  FOUNDATION 


505 


It  closely  resembles  the  Breuchaud  method  described  in  the 
following  articles,  the  essential  difference  being  that  here  needle- 
beams  were  used  temporarily  to  take  the  load. 

Horizontal  I-beams  recessed  into  the  face  of  the  wall  carried 
its  weight  to  the  transverse  24-inch  I-beams,  which  served  the 
double  purpose  of  carrying  the  weight  of  the  wall — thus  allow- 
ing deep  trenches  to  be  dug  under  the  same — and  of  furnishing 


FIG.   1656. — Method  of  Sinking    Open  Cribs  for  Underpinning,   Merchant's  and 
Trader's  Bank  Building,  New  York. 

reactions  for  sinking  the  sectional  steel  pipe  by  hydraulic  jacks. 
The  cylinders  were  sunk  to  solid  bearing,  filled  with  concrete 
and  capped  with  a  footing  wall  on  which  was  built  the  new  brick 
wall  to  connect  to  the  old  wall.  The  left-hand  illustration  shows 
a  single  cylinder,  and  the  right-hand  illustration  two  cylinders 
being  used. 

Fig.  1656  indicates  the  use  of  a  caisson  for  the  new  founda- 
tion of  a  column.  1 "  A  heavy  bracket  made  of  a  steel  plate  26 
inches  long  and  ii  inches  thick,  bent  at  right  angles,  was 

Engineering  Record,  vol.  49,  page  135,  Jan.  30,  1904. 


506  UNDERPINNING  BUILDINGS  CHAP.  XVI 

secured  to  the  street  face  of  the  column  by  five  f-inch  stud- 
bolts.  Its  longitudinal  face  took  bearing  on  the  upper  flange 
of  a  24-inch  I-beam  needle  parallel  to  the  street  line  which  was 
supported  on  a  sill  in  the  sidewalk  vault  and  on  cribbing  in  the 
excavation  for  the  new  building.  The  granite  pedestal  was 
removed,  the  concrete  footing  torn  out  and  the  excavation 
carried  down  a  little  lower  to  receive  ther  bottom  course  of  a 
timber  crib  or  caisson  36  inches  wide  and  42  inches  long  inside. 
This  course  consisted  of  four  4X1 2-inch  oak  planks  set  edge- 
wise, and  having  their  lower  sides  beveled  to  a  cutting  edge. 
They  were  connected  at  the  corners  by  short  vertical  angles 
and  had  i-inch  tie-rods  with  countersunk  heads  in  the  direc- 
tion transverse  to  the  lot  line.  The  two  sides  parallel  with  the 
lot  line  had  mortised  joints  with  the  other  two  sides,  and  the 
frame  thus  formed  was  provided  with  vertical  oak  dowels  i 
inch  in  diameter  which  projected  from  the  upper  edge  to  lock 
it  to  the  succeeding  course. 

"Timbers  were  set  on  the  upper  edges  of  the  planks,  and 
two  30-ton  jacks  seated  in  the  middle  of  them  reacted  against 
the  granite  pedestal  which  was  inserted  between  their  tops 
and  the  base  plate.  A  laborer  with  a  shovel  and  scoop  exca- 
vated the  sand  from  the  interior  of  this  caisson  as  it  was 
forced  down  by  two  other  men  operating  the  hydraulic  jacks. 
When  the  jacks  had  made  a  full  stroke,  the  pedestal  was  sup- 
ported by  cross  pieces  temporarily  inserted  under  it  and  bear- 
ing on  needle  beams  and  sills.  The  jacks  were  then  released, 
another  course  added  to  the  caisson,  the  jacks  replaced,  the 
caisson  forced  down  and  excavation  continued  and  so  on," 
.  .  .  When  the  caisson  was  sunk  to  place  the  bottom  of  the 
excavation  was  carefully  leveled  and  the  excavation  filled  with 
concrete  rammed  in  6-inch  layers. 

ART.  166.    JOINING  TO  THE  OLD  WALL 

After  needling  the  wall  and  placing  the  new  concrete  founda- 
tion, brick  piers  are  built  upon  the  new  foundation  between  the 
needles  to  within  a  few  feet  of  the  bottom  of  the  old  wall.  On 


ART.  167  THE  BREUCHAUD  PROCESS  507 

these  piers  are  placed  pairs  of  cut  stones  of  the  same  length  and 
thickness  as  the  piers,  and  about  14  inches  high.  One  stone  sets 
loosely  on  the  other,  with  pairs  of  steel  wedges  between.  The 
brick  pier  is  then  continued  on  the  upper  stones  until  the  under 
side  of  the  old  wall  is  reached,  to  which  it  is  carefully  joined. 
The  wedges  are  then  driven  together  until  the  load  is  lifted 
from  the  needles,  after  which  the  latter  are  removed  and  the 
brickwork  of  the  wall  completed,  the  final  appearance  being 
that  shown  in  Fig.  i6$a.  The  wedges  are  then  sawed  off  flush 
with  the  faces  of  the  wall  and  the  space  between  the  cut  stones 
filled  with  grout.  Theoretically,  the  entire  load  is  carried 
through  the  wedges  but  actually  some  settlement  doubtless 
occurs  to  distribute  the  load  throughout  the  length  of  the 
wall. 

The  caisson  foundation  shown  in  Fig.  1656  was  joined  to 
the  column  as  follows:  iaThe  top  of  the  caisson  was  covered 
by  heavy  flagstones  set  so  as  not  to  bear  on  the  timber  walls, 
and  on  them  a  brick  pier  was  built  up  nearly  to  the  height  of 
the  granite  pedestal  and  capped  with  a  cut  granite  block,  be- 
tween which  and  the  pedestal,  pairs  of  steel  wedges  were  driven 
until  the  weight  of  the  column  was  transferred  from  the  needle 
beam  to  the  new  footing." 

ART.  167.  THE  BREUCHAUD  PROCESS 

The  Breuchaud  process  of  underpinning  consists  of  sinking 
a  series  of  cylinders  in  the  plane  of  the  wall  and  spaced  a  few 
feet  apart.  They  are  sunk  to  hard-pan  or  rock  and  form  the 
support  for  the  wall.  The  work  is  carried  out  in  the  following 
order:  First,  horizontal  and  vertical  recesses  are  cut  in  the 
wall  near  its  foot;  second,  horizontal  bearing  beams  and  verti- 
cal steel  cylinders  are  placed  in  these  recesses;  third,  the  cylin- 
ders are  forced  down  to  solid  bearing  by  jacking  against  the 
under  side  of  the  horizontal  beams  and  by  excavating  the 
material  from  the  interior  of  the  cylinder;  and  fourth,  the 
cylinders  are  then  filled  with  concrete  and  wedged  against  the 

1  Engineering  Record,  vol.  49,  page  135,  Jan.  30,  1904. 


508  UNDERPINNING  BUILDINGS  CHAP.  XVI 

horizontal  beams,  thus  transferring  the  weight  of  the  wall  from 
the  original  supports  to  rock  or  hard-pan. 

This  method  possesses  the  following  advantages  over  the 
needle-beam  method:  First,  it  occupies  less  space;  second,  it 
makes  it  unnecessary  to  enter  the  basement  of  the  building, 
the  cutting  being  done  from  the  outside  and  usually  not  en- 
tirely through  the  wall;  and  third,  it  is  cheaper  if  the  founda- 
tion is  to  be  carried  down  a  considerable  distance.  In  general 
it  may  be  said  that  for  shallow  underpinning  the  needle-beam 
method  is  preferable;  while  for  deep  work  the  Breuchaud 
method,  or  a  modification  of  the  same,  is  better. 

The  Breuchaud  process  may  be  divided  into  two  systems,  the 
pipe  and  the  cylinder.  The  essential  difference  in  the  opera- 
tion of  the  two  systems  lies  in  the  fact  that  workmen  can  enter 
the  cylinders  but  not  the  pipes. 

DESCRIPTION  OF  SHELLS. — The  shells  are  usually  made  with 
a  cutting-edge  section  of  steel,  and  with  other  sections  of  steel 
or  cast  iron.  The  sections  are  from  4  to  8  feet  in  length,  and 
when  of  cast  iron  are  flange-bolted  on  the  inside;  when  of  steel 
they  may  be  flange-bolted  or  fastened  with  a  screw  joint. 

The  load  to  be  carried  or  the  necessity  for  workmen  to  enter 
the  cylinder  determines  their  diameter.  The  magnitude  of  the 
load  to  be  taken  by  a  cylinder  depends  upon  the  weight  of  the 
wall  per  linear  foot  and  the  spacing  of  the  cylinders.  The 
shells  are  usually  designed  to  take  all  the  load,  no  reliance  being 
placed  on  the  concrete  filling  to  assist  in  carrying  it,  the  reason 
for  this  being  that  the  load  is  placed  on  the  cylinders  before  the 
concrete  hardens.  The  spacing  of  the  cylinders  cannot  vary 
between  wide  limits,  for  on  the  one  hand  there  must  be  a  clear- 
ance between  cylinders  sufficient  to  furnish  proper  bearing 
area  on  the  soil  while  the  piers  are  being  sunk,  while  on  the 
other  hand  the  maximum  spacing  is  limited,  owing  to  the  local 
concentrated  stresses  involved  in  carrying  the  load  from  the 
wall  to  the  cylinder.  The  usual  spacing  of  cylinders  is  from 

5  to  12  feet.     The  cylinders  may  vary  in  diameter  from  about 

6  inches,  carrying  a  load  of  from  30  to  40  tons  each,  to  3  or 
4  feet,  carrying  a  load  as  high  as  400  tons.     A  double-shell 


ART.  167 


THE   BREUCHAUD   PROCESS 


509 


cylinder  is  sometimes  used,  in  which  case  added  strength  is 
developed  by  breaking  horizontal  joints. 

If  workmen  are  to  enter  the  cylinder  the  latter  should  have 
a  diameter  of  at  least  30  inches.  This  will  be  desirable  where 
boulders  are  encountered,  where  sinking  must  be  done  through 
hard-pan,  or  where  it  is  desired  to  carefully  prepare  the  bottom 
on  completion  of  sinking.  The  work  in  the  cylinder  must 
usually  be  done  under  air  pressure  and  hence  they  are  made 
so  as  to  be  easily  transformed  into  pneumatic  caissons. 

In  Fig.  1670  is  shown  the  lower  riveted  steel  section  of  the 
cylinders  and  the  air-lock  used  in  underpinning  the  Stokes 
Building,  an  eleven-story  structure  having  a  wall  load  of  45  tons 
per  linear  foot.  The  top  of  this  section  was  .faced  to  receive 
the  bottom  of  the  lowest  of  the  cast-iron  sections,  which  were 
made  in  6-foot  lengths  ordinarily,  with  special  2-  and  4-foot 
lengths  to  finish  out  with.  The  flange  connections  were  made 
with  twenty-eight  i-inch  steel  bolts,  and  were  machine  faced 
to  give  a  clearance  in  order  to  prevent  bearing  of  flanges, 
so  that  the  pressure  would  be  transmitted  directly  through 
the  shells  of  the  cylinder.  The  cylinders  were  built  up  to  the 
required  height  and  on  the  upper  sections  were  placed  the  steel- 
plate  bearing  rings  to  receive  the  girders  on  which  rested  the 
jacks.  The  5-inch  pipe  carried  away  the  material  washed  out. 

On  reaching  hard-pan  the  bearing  ring  was  removed  and  there 
was  inserted  between  the  flanges  of  the  last  two  sections  a 
heavy  cast  diaphragm.  A  similar  one  was  also  placed  on  top 
of  the  upper  section.  The  top  section  was  then  made  to  serve 
as  an  air-lock  by  fitting  steel  doors  with  rubber  gaskets,  to  the 
under  sides  of  the  diaphragms. 

The  cylinders  used  in  underpinning  the  Trust  Company  of 
America  Building,  New  York  City,  were  made  entirely  of 
steel  and  were  3  feet  in  diameter,  with  two  longitudinal  lock- 
bar  joints.  The  metal  was  f  inch  thick.  Each  section  had 
horizontal  circular  angles  riveted  to  it  at  both  ends  to  provide 
flanges  for  connecting  the  successive  sections. 

In  some  underpinning  at  No.  73-75  East  54th  Street,  New 
York,  cylinders  of  f-inch  steel  and  12  inches  in  diameter  were 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


7. 

C 

0 

V 

c 

a 
a 

bj|« 

j 

i—"    0 

s                                                                        \ 

/                 5 

*      ° 

ART.  1 68 


METHOD   OF   SINKING   CYLINDERS 


used.  They  were  first  set  up  in  20-foot  lengths.  x"As  these 
were  jacked  down  the  upper  sections,  4  feet  long,  were  coupled 
to  them  by  inside  cast-iron  sleeves  about  f  inch  thick  and  9 
inches  long,  slightly  tapered  at  the  ends  to  enter  the  pipe  and 
having  a  horizontal  exterior  rib,  about  i  inch  wide,  and  of  the 
same  thickness  as  the  pipe,  on  the  center  line.  The  edges  of 
the  rib  were  slightly  beveled  so  that  the  ends  of  the  pipe  would 
draw  up  against  it  and  make  a  solid  contact  undef  heavy  pres- 
sure, thus  insuring  a  perfect  fit  and  very  rapid  assembling  of 
the  pipe  sections  as  the  work  progressed." 


ART.  1 68.     METHOD  OF  SINKING  CYLINDERS 

The  cylinders  are  sunk:  First,  by  means  of  hydraulic  or 
screw  jacks  bearing  against  the  wall  above  and  forcing  them 
down;  second,  by  using  a  water-jet  on  the  inside  of  the  cylinder 
to  loosen  the  material  around  the  cutting  edge;  and  third,  by 
excavating  the  material  from  the  inside. 

A  horizontal  recess  of  a  size  sufficient  to  receive  I-beams  is 
first  made  in  the  wall  about  12  feet  above  its  base.  I-beams  are 
then  placed  in  it  and  wedged  up  tightly  against  the  top,  after 
which  a  vertical  recess,  extending  from  the  horizontal  recess 
to  the  foot  of  the  wall,  is  cut  out.  The  horizontal  beams  serve 
the  double  function  of  carrying  the  weight  of  the  wall  above  the 
vertical  recess  and  acting  as  a  reaction  for  the  jacks  used  in 
sinking  the  cylinders.  On  completion  of  the  vertical  recess 
the  lower  section  of  the  cylinder  is  placed  in  position  in  the 
recess.  A  screw  or  hydraulic  jack  is  then  placed  on  the  section 
and  forces  the  cylinder  down  by  reacting  against  the  horizon- 
tal I-beams  through  blocking.  As  soon  as  the  cylinder  has 
been  forced  down  a  distance  equal  to  the  full  stroke  of  the 
jack  more  blocking  is  placed  between  the  latter  and  the  bear- 
ing beams,  and  the  operation  repeated.  On  completion  of  the 
sinking  of  one  section  of  the  cylinder  another  section  is  added 
and  the  operation  repeated  until  the  cutting  edge  has  reached 
the  desired  position. 

1  Engineering  Record,  vol.  64,  page  276,  Sept.  2,  1911. 


512 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


In  the  case  of  the  larger  cylinders  fitted  for  pneumatic  pres- 
sure, they  are  sunk  as  far  as  possible  by  washing  out  the 
material,  assisted  perhaps  by  a  sand  pump;  the  doors  are 
then  put  on  and  the  remainder  of  the  sinking  is  done  by  the 
pneumatic  process.  At  the  same  time  jacks  are  operated  to 
force  the  cylinder  down.  In  the  case  of  the  smaller  pipes  the 
material  is  sometimes  bored  out  with  an  auger,  a  g-inch  auger 
being  used  fbr  a  lo-inch  pipe. 

The  following  description,  together  with  that  given  in  Art. 
167,  shows  the  method  used  in  placing  the  cylinders  for  the 
Stokes  Building,  this  being  the  first  large  structure  in  which  the 


Brick 


Wall 

of 

Stokes 
Building 


Concrete 


Elevation.  Isometric    View. 

FIG.   i68a. — Recesses  Cut  in  the  Wall  for   Underpinning. 

Breuchaud  method  of  underpinning  was  applied,  the  work 
being  done  in  1896.  Recesses  of  the  form  shown  in  Fig.  i6Sa 
were  cut  in  the  wall  to  a  depth  of  3  feet,  the  material  in  the  upper 
horizontal  rectangle  being  first  removed.  Five  i5~inch  I- 
beams  were  then  placed  in  this  opening  and  wedged  tightly 
against  the  upper  surface  of  the  recess.  The  vertical  rec- 
tangular recess  was  then  cut  out.  A  section  of  the  cylinder  was 
then  placed  in  the  vertical  recess  and  on  it  were  placed  two 
I-beams  34  inches  long.  On  these  I-beams  rested  a  large 
hydraulic  jack  which  took  bearing  on  the  1 5-inch  I-beams 
above  through  timber  blocking.  As  the  cylinder  was  jacked 
down  the  material  inside  was  washed  out  with  a  jet  pipe. 


ART.  169 


CONCRETING  THE   CYLINDERS 


513 


ART.  169.     CONCRETING  THE  CYLINDERS 


Curb  Ef.0.0 


'.'}'.-•  '•;*-•  v-1; 

ili 


-OricrJnat 
Footing-Mills 
Building 


Wafer 


hi 


FIG.  1690. — Typical  Underpinning  Cylin- 
der for  Mills  Building,  New  York. 


33 


Where  pipes  are  used  little 
can  be  done  in  preparing  the 
bottom  further  than  to  inspect 
it;  to  pump  out  the  water  if 
possible;  and  to  see  by  means 
of  an  electric  light  if  the  de- 
sired bearing  has  been  reached 
and  that  all  loose  material  has 
been  removed.  On  the  other 
hand,  with  the  larger  cylinders  the  bottom  can 
be  cleaned  and  leveled  off,  and  the  foundation 
bearing  extended  if  desired.  This  was  done  in 
the  Old  Mills  Building  of  New  York,  by  spread- 
ing out  the  opening  through  the  hard-pan  to  a 
maximum  diameter  of  5  feet  6  inches.  Radial 
steel  grillage  beams,  Fig.  1690,  resting  on  a 
concrete  footing,  took  the  load  from  the  cylin- 
der through  steel  wedges. 

A  1-2-4  concrete  is  ordinarily  used  for  the 
cylinder  filling.  For  pipe  cylinders  the  con- 
crete must  very  often  be  placed  through  water. 
To  insure  a  rich  mixture  at  the  bottom  it  is 
advisable  first  to  pump  in  some  grout  or  to 
drop  in  some  dry  cement,  and  on  this  to  place 
the  concrete.  After  placing  a  few  feet  of  the 
concrete  and  allowing  it  to  harden,  the  pipe 
may  be  pumped  out  and  the 
remainder  of  the  concrete  laid 
in  the  dry.  Where  deposited 
through  water  a  cylindrical 
bucket  of  a  diameter  somewhat 
smaller  than  that  of  the  pipe 
and  about  3  feet  long  is  often 
used.  The  bucket  has  a  flap 
bottom,  and  two  lines,  one 


Top  of  H&rd  Pprn 


ftac/ic*/  Steel 
frrillage  Beams 


Pock,  El.  -65.0 

'—  -$>-6"---?>\  '       EN&.N! 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


attached  to  the  bail  of  the  bucket  and  the  other  to  the  flap. 
In  lowering  the  bucket  the  weight  is  carried  by  the  flap  line 
but  after  the  bucket  is  seated  on  the  bottom  it  is  pulled  up 
by  the  bail  line,  which  causes  the  concrete  to  be  deposited 
through  the  bottom.  This  avoids  any  possibility  of  the  water 
washing  the  concrete  and  separating  the  constituent  materials. 
For  pneumatic  cylinders  the  working  chamber  is  first  filled 
with  concrete,  with  perhaps  a  layer  of  grout  or  mortar  on  the 
bottom,  after  which  the  air  pressure  is  left  on  for  about  48  hours. 
The  remainder  of  the  cylinder  is  then  filled  with  concrete. 


ART.  170.     TRANSFERRING  LOAD  TO  CYLINDER 

Fig.  170^  illustrates  the  method  used  in  transferring  the 
loads  to  the  cylinders  in  the  Empire  Building,  New  York. 
The  underpinning  cylinders  were  first  capped  and  the  recess 
_  ,  ,  .  ,  ,  ,  above  them  filled  with  brick  work 

to  a  certain  height.  On  this 
brickwork  two  granite  blocks 
were  placed,  one  resting  loosely 
on  the  other,  after  which  the 
remainder  of  the  brickwork  was 
placed.  Pairs  of  steel  wedges 
were  then  inserted  between  the 
granite  bearing  blocks  and 
driven  together,  thus  separating 
the  two  blocks  and  bringing  the 
wall  loads  to  the  cylinders.  The 

FIG.  1700.— Underpinning  the  Empire    «,nflrp    Kptwppn    tViP    hlort«i   wac 
Building,  New  York.  "l  WC(  |OCKS   WaS 

then  filled  with  cement  grout. 

After  the  cylinders  of  the  Stokes  Building  had  been  filled 
with  concrete  the  top  of  each  cylinder  was  capped  with  a  top 
bearing  plate  (Fig.  1670.)  Five  I-beams  were  then  placed  on 
the  top  of  each  cylinder  as  shown  in  Fig.  1706.  Steel  posts 
were  placed  in  the  vertical  recess  and  rested  on  steel  plates 
which  in  turn  rested  on  the  lower  tier  of  I-beams,  the  posts 
extending  to  within  2  inches  of  the  under  side  of  the  upper  tier 


ART.  171 


OTHER  MODERN  METHODS 


515 


of  I-beams  previously  placed  (Art.   168).     Steel  plates  were 

placed  on  these  posts  and  pairs  of  forged  steel  wedges  then 

driven    together    between 

these  plates  and  the  lower     stokes  Bui/ding 

surface  of  the  upper  tier 

of  I-beams   to  bring   the 

wall  load  to  the  cylinder. 

After  this  the  recess  was 

solidly  bricked  up. 

The  lower  tier  of  I- 
beams  serves  a  triple  pur- 
pose: First,  it  reduces 
the  amount  of  load  com- 
ing through  the  upper 
tier,  thus  lessening  the 
stress  in  the  brickwork  at 
that  point;  second,  it  car- 
ries the  weight  of  the 
wall  below  the  upper  tier 
of  beams  to  the  pier, 
where  it  must  otherwise 
remain  on  the  old  foot- 
ing; and  third,  it  elimi- 
nates stress  in  the  new 
brickwork  in  the  vertical 
recess. 


5-' 'Bea 

'  /        j  'S/ 

•'?->,'',ncirdpa 
Part  Elevation. 


im#^/ 
m$& 
fyffiffi'. 


Cross  Section. 


FIG.  1706. — Underpinning  the  Stokes  Build- 
ing, New  York  City. 


ART.  171.     OTHER  MODERN  METHODS' 

Another  method  of  underpinning,  developed  to  cheapen 
the  cost  and  reduce  the  risk  in  many  cases,  especially  where 
the  building  to  be  underpinned  is  light  or  poorly  constructed, 
is  to  sink  shafts  with  plates,  as  was  done  in  underpinning  the 
Cambridge  B  uilding,  New  York  City. 

iaThe  cylinders  (Fig.  1710)  were  4  feet  in  diameter,  and  had 


Underpinning  the  Cambridge  Building,  New  York  City,  by  T.  K.  THOMSON 
Trans.  Am.  Soc.  C.  E.,  vol.  67,  page  553. 


UNDERPINNING  BUILDINGS 


CHAP.  XVI 


very  thin  shells.  The  method  of  placing  them  constitutes  a 
new  system  of  underpinning;  for,  instead  of  placing  the  bottom 
section  first  and  jacking  it  into  the  ground,  and  then  plac- 
ing another  section  on  top  and  repeating  the  operation, 


40 


Sectional  Plan,  Enlarqed. 

All  Plates  to  have  square  Edges  flush  with  Heel 
of  Angle.  /Ill  Angles  2%  "*2i  "x  %'.  All  Rivets  £  "Diam., 
Heads  Flattened  Outside.  All '  open  Holes  ~"Diam, 

Each  Shaft  ft  be  put  down  as  a  Vertical  Tunnel, 
Using  Poling  Boards  if  necessary,  and  Compressed 
Air  if  Water  is  encountered.  Spaces  behind 5hells 
to  be  filled  with  6 rout. 


j 

Top 

is 

'i  
$ection 

is,?i'*ttW 

^ 
41 

\ 
j  

--..  -1 

T^PIates 

§S^ 
« 
4 


FIG.   lyia.  — 


Elevation. 
Underpinning    by    THOMSON'S    Method    of    Vertical    Tunneling. 

a  space  was  excavated  for  the  top  section,  which  was  made  4 
feet  deep,  and  the  space  outside  of  this  top  section  was  back- 
filled, generally  with  concrete,  and  remained  permanently  in 
that  position. 


ART.  171  OTHER    MODERN    METHODS  517 

"A  laborer  then  entered  the  top  section  and,  with  a  short- 
handled  shovel,  excavated  the  material  under  the  cutting  edge 
sufficiently  to  insert  one  segment  of  the  next  ring.  All  the 
rings  below  the  top  section  were  2  feet  deep  and  in  four  segments, 
one  of  which  was  small,  to  act  as  a  key,  as  in  tunnel  lining.  In 
this  key  segment  the  connection  angles  were  bent  13^  degrees 
from  the  radial,  to  permit  putting  the  key  in  place.  The 
joints  of  the  other  segments,  of  course,  were  on  the  radial  lines. 
All  the  plates  were  f\  inch  thick,  and  all  the  angles,  both 
horizontal  and  vertical,  were  2^X2|Xi  inches.  When  the 
first  segment  under  the  top  section  had  been  bolted  in  place, 
the  excavation  was  made  for  the  second  segment,  then  the 
third,  and  then  the  fourth  or  key.  Where  the  ground  was 
good,  the  excavation  was  made  for  all  four  segments  at  once." 
No  water  was  encountered  in  the  above  operation,  thus  elimi- 
nating the  necessity  for  using  air  pressure.  Where  the  latter 
is  used  all  joints  must  be  caulked. 

Another  method  patented  by  OGDEN  MERRILL,  makes  use  of  a 
nest  of  telescoped  cylinders  or  caissons.  The  upper  section  is 
first  jacked  down  and  then  the  other  sections  are  jacked  inside  of 
this,  after  removing  the  material  from  the  inside.  The  pneu- 
matic process  has  been  applied  also  to  this  form  of  construction. 


CHAPTER  XVII 
EXPLORATIONS  AND  UNIT  LOADS 

ART.  172.    TEST  PITS  AND  SOUNDING  RODS 

A  simple  method  of  examining  a  foundation  site  is  to  sink 
test  pits  by  open  excavation  somewhat  deeper  than  the  exca- 
vation otherwise  required  for  the  substructure.  Sometimes  it 
may  be  necessary  to  line  the  pit  with  sheeting  and  to  use  a 
hand  pump  to  keep  down  the  water,  but  instead  of  increasing 
the  cost  materially  on  this  account,  other  methods  may  be 
adopted.  The  principal  advantage  of  the  open  pit  consists  in 
the  possibility  of  examining  not  only  the  variation  in  character 
of  the  earth  encountered  but  in  observing  the  degree  of  its 
natural  compactness  when  in  place.  This  method  is  practi- 
cally confined  to  shallow  foundations. 

A  sounding  rod  consists  of  an  iron  rod  or  pipe,  i  or  i^  inches 
in  diameter,  which  is  driven  into  the  ground  with  a  maul, 
and  turned  after  each  blow.  It  serves  merely  to  determine 
whether  the  resistance  is  increasing  or  decreasing,  variable  or 
constant.  A  sunken  log,  boulder,  or  some  other  obstruction 
can  stop  the  driving.  The  information  thus  secured  is  so 
unsatisfactory  and  inadequate  that  it  is  frequently  misleading. 
The  rod  may  find  a  stratum  of  gravel  but  fail  to  reach  the  soft 
stratum  underneath  it,  because  the  resistance  is  so  large  that 
it  cannot  be  driven  farther.  In  one  instance,  eight  men  on  the 
handle  bar  were  unable  to  push  the  sounding  rod  over  7  feet 
into  stiff  mud  or  clay,  but  on  driving  test  piles  at  the  same  spot 
no  difficulty  was  found  in  driving  down  70- foot  piles. 

The  following  quotation  indicates  the  manner  in  which  sound- 
ing rods  are  sometimes  used  in  practice: 

"Adjacent  to  the  wooden  test  piles,  and  in  other  places,  the  soil  was 
tested  and  explored  by  driving  standard  steel  test  rods  i  inch  in  diameter 


ART.  173  BORINGS   WITH  AUGERS  519 

made  up  of  4-foot  sections  connected  by  screwed  sleeve  couplings.  They 
were  driven  by  a  1 2-pound  sledge  to  a  refusal  of  from  i  to  \  inch  for  the  last 
blow,  at  which  their  penetration  was  assumed  to  afford  a  reliable  indica- 
tion of  the  penetration  of  a  standard  tapered  concrete  pile  driven  to  the 
required  refusal." 

ART.  173.    BORINGS  WITH  AUGERS 

A  simple  and  effective  tool  to  use  in  exploring  the  site  under 
proposed  structures  consists  of  an  ordinary  wood-auger  2  inches 
in  diameter  welded  to  a  black  pipe  about  18  inches  long,  and 
which  is  connected  by  ordinary  couplings  to  1 2-foot  sections 
of  pipe.  The  handle  used  in  turning  is  2  feet  long  and  is  made 
of  two  pieces  of  f-inch  round  iron  welded  to  a  strong  ring 
that  will  pass  freely  over  the  coupling,  and  is  secured  to  the 
pipe  by  a  f  X2|-inch  set-screw. 

In  starting  the  boring  great  care  is  necessary  to  keep  the 
auger  vertical.  Five  turns  fill  the  bit,  which  is  then  with- 
drawn to  the  surface,  and  cleaned  after  examining  the  material. 
When  the  hole  is  too  deep  to  raise  the  auger  by  hand,  it  is 
lifted  by  a  block  and  fall  suspended  from  a  wooden  folding 
tripod,  a  3-foot  chain  being  used  to  grip  the  pipe.  Before 
lowering  the  chain  for  a  new  grip,  the  handle  is  attached,  so 
that  there  is  no  chance  of  the  auger  dropping  when  any  sec- 
tions of  the  pipe  have  been  removed. 

Another  auger  I  inch  in  diameter  connected  to  6-foot 
sections  of  |-inch  pipe  is  required  when  the  hole  becomes 
clogged  so  that  the  larger  auger  can  no  longer  be  used.  With 
dry  sand  it  is  necessary  to  pour  enough  water  into  the  hole  to 
make  the  grains  stick  together  that  they  may  be  lifted.  When 
sand  and  gravel  become  troublesome  and  the  hole  will  not  retain 
its  shape,  a  3-inch  casing  is  driven,  being  handled  in  4-  or  5- 
foot  lengths.  A  2-inch  drill  with  chisel  point  attached  to 
sections  of  pipe  like  the  auger,  may  also  be  needed  to  cut 
through  some  obstructions.  Borings  with  augers  have  been 
used  for  depths  up  to  100  feet. 

The  borings  are  regularly  inspected  as  the  ground  is  pene- 
trated and  a  record  kept  of  the  depths  and  variations  of  mate- 


520  EXPLORATIONS   AND   UNIT   LOADS  CHAP.  XVII 

rials  encountered.  Even  with  the  aid  of  the  casing  this  method 
of  boring  is  not  applicable  in  fine-running  gravel  or  in  quick- 
sand unless  it  is  a  thin  stratum.  The  loose  material  may  then 
be  removed  by  a  sand  pump  which  consists  of  a  narrow  cylin- 
drical bucket  with  a  cutting  edge  at  the  bottom  and  above 
this  a  flap  valve  opening  upward.  It  is  partly  filled  by  rapidly 
raising  and  dropping  it  alternately. 

One  form  of  earth  or  clay  auger  has  two  cylindrical  cutters 
pointed  and  bent  at  the  bottom,  so  as  to  draw  the  auger  into 
the  earth,  and  after  rotation,  to  support  a  lot  of  excavated 
material  during  its  withdrawal  to  the  surface.  This  tool  is 
designed  to  penetrate  compact  material  like  hard-pan  and 
frozen  earth. 

Sometimes  the  hole  will  retain  its  shape  better  if  the  di- 
ameter is  larger.  It  is  claimed  that  a  diameter  of  8  inches  is 
frequently  advantageous  for  ordinary  depths  unless  the  pro- 
portion of  sand  is  too  large.  A  post-hole  digger  may  be  used 
up  to  about  1 6  feet. 

ART.  174.    WASH  BORINGS 

When  considerable  work  is  to  be  done  a  standard  outfit  for 
wash-drill  borings  is  employed  which  consists  of  a  small  der- 
rick or  tripod,  the  casing,  hollow  drill  rods,  and  a  hand  force 
pump,  together  with  their  accessories  and  necessary  tools. 
A  convenient  size  of  tripod  has  timber  legs  3X4  inches  in 
section  and  18  feet  long.  The  rope  for  raising  and  lowering 
the  casing  and  drill  rods  is  manipulated  either  directly  by  hand 
or  with  the  aid  of  a  drum.  The  casing  is  composed  of  extra 
heavy  pipe  in  about  5-foot  lengths,  with  flush  joints  so  as  to 
form  a  smooth  exterior  surface.  The  usual  size  has  a  nominal 
inside  diameter  of  2\  inches.  The  hollow  drill  rods  are  made 
of  heavy  seamless  steel  tubing  usually  in  5-foot  lengths,  but 
sometimes  as  long  as  16  feet,  connected  by  special  coupling 
pieces  about  6  inches  long.  The  usual  size  of  drill  rod  has  an 
outside  diameter  of  ij  inches  for  a  2! -inch  casing.  To  the 
bottom  drill  rod  is  attached  a  chopping  bit  with  an  X-shaped 


ART.  174 


WASH  BORINGS 


chisel  point,  and  with  four  openings  for  the  water-jet.  The 
hand  pump  consists  of.  a  double-acting  force  pump  with  a 
single  hand  lever  and  i|-inch  suction.  The  upper  drill  rod  is 
connected  to  the  hose  from  the  pump  by  means  of  a  hoisting 
water  swivel,  so  that  it  may  be  raised  or  lowered  and  rotated 
during  operation  without  twisting  the  hose. 

During  operation  water  is  forced  down  through  the  hollow 
drill  rod,  and,  escaping  through  the  jet  at  the  bit,  carries  upward 
the  loose  material  in  the  annular  space  between  the  rods  and 
casing.  In  suitable  material  the  drill  rod  is  worked  down  by 
rotating  it.  In  harder  material  it  must  be  lowered  by  'churn- 
ing.' This  is  accomplished  by  raising  it  up  a  short  distance 
and  letting  it  drop.  Meanwhile  the  casing  is  also  worked 
down  by  rotating  it.  If  this  will  not  answer  the  purpose,  the 
casing  must  be  driven  down.  If  the  tripod  has  only  a  single 
pulley  the  drill  rods  have  to  be  withdrawn  when  the  casing  is 
to  be  driven  deeper.  By  using  a  double  block  and  a  jar  weight 
the  operation  of  driving  the  casing  may  go  on  simultaneously 
with  the  drilling  and  jetting.  In  this  manner  the  casing  is 
kept  loose.  To  protect  the  casing  a  drive  head  is  screwed  into 
the  top  section  and  into  that  a  hollow  guide  which  guides  the 
cylindrical  jar  weight  in  its  movements.  The  upper  section  of 
the  casing  has  slots  in  the  side  for  the  escape  of  the  water  and 
sediment  or  other  loosened  material.  After  the  overflow  which 
is  caught  in  a  bucket  has  settled,  samples  are  taken  and  put  in 
glass  bottles  for  preservation.  They  are  properly  labelled  to 
correspond  with  other  records. 

This  operation  is  continued  until  the  required  depth  is 
reached  or  until  obstacles  like  boulders  are  encountered.  If 
a  boulder  is  not  too  large  a  small  charge  of  dynamite  may  be 
used  by  an  experienced  operator,  care  being  taken  to  raise  the 
casing  high  enough  to  avoid  any  damage  from  the  explosion. 
With  this  equipment  borings  _can  be  made  in  sand,  gravel,  clay, 
in  varying  degrees  of  hardness,  including  indurated  clay 
and  hard-pan.  For  borings  into  rock,  shot  drills  or  diamond 
drills  are  required. 

When  only  a  small  amount  of  work  is  to  be  done  and  in  light 


522  EXPLORATIONS   AND  UNIT   LOADS  CHAP.  XVII 

or  sandy  material,  a  less  expensive  outfit  may  be  employed. 
Ordinary  pipe  can  be  used  for  the  casing,  a  good  size  being  2 
inches  in  diameter.  Gas  or  water  pipe  f  inch  in  diameter  may 
be  substituted  for  the  hollow  drill  rods,  with  a  water  swivel 
made  of  ordinary  bends  and  nipples.  Lighter  chopping  bits 
may  be  used.  Sometimes  the  bit  has  only  a  single  chisel  point 
with  an  opening  on  each  side  for  the  jet,  or  the  bit  may  be  re- 
placed by  a  plain  jet  pipe.  In  silt  and  some  mixtures  of  clay 
and  sand,  it  may  not  be  necessary  always  to  have  the  casing 
follow  the  inner  pipe  to  its  full  depth  as  the  material  will  retain 
the  shape  of  the  hole.  In  sand  and  gravel  both  pipes  must  be 
sunk  together,  pains  being  taken  to  keep  them  turning  and  occa- 
sionally to  lift  the  inner  pipe  a  little  to  prevent  it  from  binding. 
In  some  instances  the  casing  has  teeth  cut  into  the  end 
of  its  lower  section  which  is  also  flared  out  slightly.  This  will 
facilitate  sinking  by  rotation,  but  little,  if  any,  hammering 
being  required. 

Since  only  the  finer  material  may  be  washed  up  while  the 
coarser  material  is  pushed  aside  in  the  hole  which  is  scoured 
out  by  the  jet,  it  is  possible  to  misinterpret  the  indications  of 
wash  borings.  In  order  to  obtain  samples  of  the  material  pene- 
trated in  its  natural  relation,  the  bit  or  jet  may  be  re- 
placed temporarily  by  a  short  piece  of  brass  pipe  which  is  then 
pressed  into  the  softened  ground  at  the  bottom  and  lifted 
out  for  examination. 

It  is  not  always  possible  to  distinguish  between  a  large 
boulder  and  bedrock.  By  making  a  number  of  borings  on 
different  parts  of  a  foundation  site  and  comparing  the  eleva- 
tions of  the  supposed  rock  surface  it  may  be  assumed  that 
unless  these  are  nearly  at  the  same  level,  the  higher  erratic 
elevations  may  indicate  boulders.  Additional  borings  should 
be"  made  near  these  locations  to  see  whether  greater  penetra- 
tions can  be  obtained. 

Since  the  action  of  the  jet  and  of  the  chopping  bit  often 
radically  change  the  natural  condition  of  some  material  pene- 
trated, it  is  desirable  to  take  out  dry  samples  or  cores  whenever 
feasible.  This  can  be  done  in  the  hardest  clay  or  the  softer 


ART.  174  WASH  BORINGS  523 

shales  by  using  a  saw-tooth  bit  working  dry.  and  thus  obtain  a 
perfect  knowledge  of  the  material.  Unless  this  is  done  a  hard 
clay  which  is  suitable  in  every  way  for  a  foundation  bed  may 
be  passed  by,  and  thus  incur  unnecessary  extra  expense  to  carry 
the  foundation  to  a  lower  level. 

Although  in  some  cases  the  results  obtained  by  wash  borings 
alone  may  be  only  negative  their  use  in  conjunction  with  core 
borings  for  the  balance  of  the  depth  required  may  save  expense 
by  materially  reducing  the  number  of  core  borings. 

The  records  of  test  borings  should  show  the  kinds  of  material, 
the  thickness  of  various  strata,  the  elevation  of  ground  water, 
etc.  By  comparing  these  data  for  various  parts  of  the  site  it 
can  be  seen  whether  any  given  stratum  is  fairly  uniform  in 
thickness  or  runs  out  between  two  borings;  and  which  stratum 
should  be  selected  to  bear  the  given  load,  or  to  receive  some 
further  test  by  loading  if  necessary. 

As  an  illustration  of  the  information  furnished  by  borings 
and  what  its  effect  was  upon  the  construction  of  the  founda- 
tion, reference  is  made  to  Eng.  News,  vol.  68,  page  914,  Nov. 
14,  1912.  The  site  of  the  Brooklyn  anchorage  pier  of  the  Man- 
hattan bridge  was  explored  by  nine  preliminary  test  borings 
which  indicated  sand,  gravel,  boulders  and  clay  in  irregular 
strata  down  to  rock  at  a  depth  of  70  to  75  feet  below  mean 
high  water.  Tests  of  the  ground  were  made  by  loading  it  and 
by  driving  piles,  and  from  a  study  of  all  these  results  and  the 
surrounding  conditions  it  was  decided  to  drive  bearing  piles 
to  carry  the  foundation  load. 

An  analysis  of  cost  for  wash-drill  borings  made  in  Resi- 
dency No.  5  of  the  New  York  State  Barge  Canal  may  be  found- 
in  a  valuable  article  by  EMILE  Low  in  Eng.  News,  vol.  57, 
page  54,  Jan.  17,  1907.  The  analysis  includes  14  items  of  cost, 
and  the  total  cost  per  linear  foot  of  boring  for  17  monthly  ac- 
counts and  several  field  parties,  ranges  from  17.55  to  52-^3 
cents,  the  average  being  36.97  cents.  The  average  depth  of 
hole  is  27.7  feet.  The  cost  given  does  not  include  that  of  the 
plant  nor  that  of  extraordinary  repairs,  for  which  an  addition 
should  be  made  estimated  at  2  cents.  The  cost  of  the  outfit 


524  EXPLORATIONS   AND   UNIT   LOADS  CHAP.  XVII 

and  tools  required  for  each  party  was  $277.98.  The  article 
gives  a  full  description  of  the  equipment,  copies  of  the  forms 
used  for  records  and  reports,  and  the  character  of  the  material 
penetrated  for  each  account. 

The  costs  for  similar  borings  made  on  the  Deep  Waterways 
Surveys  in  the  same  state  during  1897  to  1900,  are  11.2, 
13.0,  25.1,  54.1,  68.4,  70.6  and  85.2  cents  per  foot  for  different 
routes  or  divisions.  The  borings  varied  in  depth  from  a  few 
feet  to  190  feet. 

ART.  175.     CORE  DRILLING  WITH  DIAMONDS 

Rock  strata  are  tested  by  using  core  drills  to  remove  specimens 
of  the  rock  in  the  form  of  cores  which  can  be  examined.  In 
some  of  these  drills  the  cutting  is  done  by  black  diamonds,  in 
others  by  chilled  shot  or  crushed  steel,  and  in  still  others  by 
toothed  cutters. 

In  the  operation  of  a  diamond  drill  a  hollow  bit  is  rotated 
rapidly,  in  which  two  rows  of  diamonds  are  set  around  the  edge 
in  such  a  manner  that  all  the  cutting  is  done  by  them  and  with 
a  small  clearance  both  inside  and  outside.  Water  is  forced 
down  through  the  hollow  drill  rods  and  bit  to  keep  the  latter 
cool,  and  in  passing  up  outside  of  them  carries  the  cuttings  to 
the  surface.  The  bit  is  screwed  to  the  core  barrel  and  that  in 
turn  to  the  drill  rods.  The  bit  cuts  an  annular  channel  and 
the  core  formed  within  it  is  protected  by  the  descending  core 
barrel.  At  intervals  the  core  is  broken  off  by  a  special  device 
and  lifted  out  along  with  the  barrel.  Two  kinds  of  black 
diamonds  are  used  for  this  work,  carbons  being  set  for  cutting 
hard  rock,  and  bortz  for  soft  rock.  The  bort  is  as  hard  as  the 
carbon  but  not  so  tough.  For  medium  rock  half  carbon  and 
half  bortz  may  be  used. 

In  practice  it  is  customary  to  let  diamond  drill  work  for 
foundations  by  contract  as  operators  of  skill  and  experience 
are  required.  Drilling  machines  are  manufactured  of  different 
designs  and  in  a  number  of  sizes,  operated  in  most  cases  by  power. 
The  diameter  of  core  varies  from  i  to  2  inches  for  foundation 


ART.  175  CORE  DRILLING  WITH  DIAMONDS  525 

purposes,  larger  sizes  of  core  being  removed  in  wells,  tunnels, 
and  deep  mine  prospecting. 

If  surface  material  overlies  the  rock  it  must  first  be  pene- 
trated by  the  method  of  wash  borings  as  described  in  the 
preceding  article  and  the  casing  driven  into  the  surface  of  the 
rock,  making  a  tight  joint  to  exclude  the  entrance  of  sand  or 
clay.  The  diamond  drill  may  then  be  set  up  over  the  casing 
and  operations  continued. 

The  following  statement  is  quoted  from  an  article  by  Resi- 
dent Engineer  F.  H.  BAINBRIDGE  in  Mine  and  Quarry  for 
Oct.,  1908,  regarding  the  borings  made  for  the  Chicago  and 
Northwestern  Railway  bridge  over  the  Mississippi  River  at 
Clinton,  la.  The  equipment  was  mounted  on  a  scow.  The 
diamond  drill  operated  2-inch  core  bits.  Both  standpipe  and 
casing  had  flush  joints,  their  diameters  being  4!  and  3  inches 
respectively. 

"The  materials  encountered  were  in  order  as  follows:  Recent  alluvial 
sands,  glacial  drift  of  gravel,  sand  and  boulders,  a  shale  consisting  of  sand 
with  a  clay  matrix,  and  finally  limestone  bedrock.  The  upper  stratum 
of  bedrock  was  identified  by  fossils  and  general  appearance  as  belonging 
to  the  Gower  stage  of  the  Niagara  series  of  Silurian  rocks.  This  overlaid 
conformably  rock  of  the  Delaware  stage  of  the  same  series.  In  the  middle 
of  the  river  the  Gower  rock  and  nearly  50  feet  of  the  Delaware  rock  had 
been  entirely  eroded.  Great  care  was  taken  to  ascertain  the  possible  ex- 
istence of  subterranean  pockets  or  overhanging  cliffs  in  the  rock.  Only 
two  of  these  pockets  were  found,  however,  both  in  the  same  boring,  and 
these  were  only  i  and  6  inches  in  depth.  Both  were  filled  with  sand,  con- 
sisting of  about  equal  parts  of  quartz  and  dolomite  sand.  Some  of  the 
borings  were  carried  down  30  to  40  feet  into  the  bedrock  to  determine  the 
possible  existence  of  these  subterranean  pockets. 

"  All  the  boulders  encountered  were  such.as  could  be  easily  broken  with 
the  chopping  bit  and  no  dynamite  was  found  necessary.  To  determine 
the  consistency  of  the  shale,  cores  were  taken  out  with  saw-tooth  bits 
working  dry,  showing  perfectly  the  consistency  of  the  material.  The 
saw-tooth  bit  or  the  chopping  bit  working  with  the  pump  gave  no  idea 
of  what  this  material  was,  and  without  the  expedient  of  the  dry  core  an 
excellent  foundation  would  have  been  overlooked,  and  a  foundation  sought 
30  feet  lower. 

"Borings  in  the  limestone  were  made  with  a  bortz  bit  when  the  water 
was  still,  and  with  the  chopping  bit,  taking  occasional  cores  with  the  saw- 


526  EXPLORATIONS   AND  UNIT   LOADS  CHAP.  XVII 

tooth  bits.  Fully  95  percent  of  the  borings  in  the  limestone  were  made 
with  the  bortz  bit.  The  aggregate  length  of  casing  put  down  was  692 
feet,  and  that  of  casing  driven  through  hard  material  was  406.5  feet. 
The  aggregate  length  of  borings  in  shale  was  86  feet,  and  in  limestone, 
226  feet.  The  cost  was  as  follows:  Labor,  $456.16;  coal,  $124.41;  deprecia- 
tion of  bortz,  estimated,  $200.00;  scow,  $287.24;  and  depreciation  in 
tools,  pipe,  etc.,  $200.00;  total,  $1267.81.  The  scow  still  has  value  which 
is  somewhat  uncertain.  Omitting  this  credit,  the  cost  of  the  work 
amounted  to  $1.83  per  foot." 

In  exploring  for  the  tower  foundations  of  the  Williams- 
burgh  bridge,  wash  borings  were  first  made,  the  pipe  being 
driven  to  what  appeared  to  be  rock,  and  then  a  dynamite  car- 
tridge was  exploded.  If  the  pipe  could  not  be  driven  farther 
after  the  explosion  it  was  at  first  assumed  that  bedrock  was 
reached.  Upon  making  diamond  drill  borings  it  was  found  that 
instead  of  50  feet  to  bedrock  on  the  New  York  side,  the  true 
depth  varied  from  46.1  to  68.3  feet;  and  on  the  Brooklyn  side, 
instead  of  75  to  80  feet,  it  varied  from  80  to  104  feet.  In  nearly 
every  case  the  wash  borings  had  met  a  large  boulder,  and  the 
charge  of  dynamite  was  not  sufficient  to  break  it.  The  diamond 
drilling  was  extended  from  10  to  20  feet  into  the  rock. 

A. summary  of  Experience  in  Diamond  Drill  Work  on  the 
Deep  Waterways  Survey  with  Statistics  of  Cost  is  published 
in  Engineering  News,  vol.  50,  page  83,  July  23,  1903.  The 
data  relate  to  25  holes  of  an  average  depth  of  98.5  feet.  The 
conditions  under  which  the  work  was  done  are  described  and  the 
special  difficulties  noted.  The  total  carbon  loss  is  25^  carats 
in  drilling  1688  feet  of  rock,  making  the  cost  for  diamonds 
47.7  cents  per  foot,  at  $36.50  per  carat.  The  rate  for  drilling 
in  different  kinds  of  rock,  in  feet  per  hour,  is:  quartzite  1.7; 
limestone,  2.5;  sandstone,  3.0;  and  shale,  5.0.  The  distribution 
of  time  is  as  follows: 

Sinking  casing     325  hours  17  percent 

Drilling  rock 753  hours  41  percent 

Delays 386  hours  20  percent 

Moving  (38  times) 356  hours  19  percent 

Holidays  and  storms 60  hours  3  percent 

Total. .                 1880  hours  100  percent 


ART.  176 


CORE  DRILLING  WITHOUT  DIAMONDS 


527 


The  delays  due  to  moving  were  unusually  high  on  account  of 
frequent  and  long  moves,  as  well  as  bad  weather  and  delays 
in  getting  cars. 

The  total  length  of  casing  sunk  was  552  feet,  and  of  holes 
drilled  in  rock,  1910  feet.  The  general  average  depth  sunk  per 
day  of  10  hours  is  therefore  13.1  feet  when  moving  and  other 
delays  are  included,  and  16.2  feet  when  the  time  for  moving  is 
excluded.  While  actually  working,  the  rate  of  sinking  the  cas- 
ing through  sand,  gravel,  etc.,  was  17.0  feet,  and  of  drilling  in 
rock,  25.3  feet  per  zo-hour  day.  The  analysis  of  cost  is  given 
including  13  items,  the  total  cost  per  foot  averaging  $3.137. 

ART.  176.     CORE  DRILLING  WITHOUT  DIAMONDS 

The  increasing  demand  for  black  diamonds  for  diamond 
drilling  in  mine  prospecting  and  for  other  purposes  led  to  such 
a  rise  in  price  as  to  exceed  tenfold  the  cost  when  the  core  drill 
was  first  practically  developed.  This  naturally  led  to  the  in- 
vention of  core  drills  without  the  use  of  diamonds.  In  one 
type  of  such  drills,  chilled  steel  shot  are  made  to  travel  under  a 
hollow  soft  steel  bit  which  rotates  and  exerts  a  pressure  on  the 
shot  at  the  same  time,  thereby  causing  them  to  mill  away  the 
rock.  The  bit  is  screwed  to  the  core  barrel  and  that  is  screwed 
to  the  hollow  drill  rods  as  in  diamond  drills.  One  side  of  the 
bit  has  a  V-shaped  or  diagonal  slot  in  it  to  aid  the  shot  in  work- 
ing freely  under  the  bit  and  to  permit  some  of.  the  water  from 
the  jet  to  escape  without  passing  under  the  edge  of  the  bit. 

Another  special  feature  of  one  make  of  shot  drill  is  the  calyx 
or  sludge  receiver.  It  is  formed  by  a  tube  surrounding  the 
drill  rods  above  the  core  barrel,  in  which  are  deposited  the 
chips  or  sludge  on  account  of  the  sudden  decrease  in  velocity 
of  the  upward  current  of  water.  The  cuttings  thus  received 
form  a  duplicate  record  of  the  strata  penetrated.  If  sufficient 
water  is  used  to  bring  the  cuttings  to  the  surface,  its  velocity 
is  so  great  as  to  wash  the  shot  away  from  under  the  bit. 

The  sizes  of  cores  cut  by  shot  drills  are  generally  larger 
than  those  of  diamond  drills  and  range  from  i|  to  20  inches. 


528  EXPLORATIONS   AND  UNIT   LOADS  CHAP.  XVII 

The  largest  cores  are  required  for  other  purposes  than  founda- 
tion explorations.  Cores  4  to  5  inches  in  diameter  can  be 
extracted  as  cheaply  as  those  of  2  inches  or  less  while  the  rate 
of  progress  is  as  good  or  better  than  for  the  smaller  cores. 
Except  for  the  very  hardest  rocks  the  shot  drill  is  found  to  be 
more  economical  than  the  diamond  drill. 

The  successful  operation  of  the  drill  requires  the  proper 
regulation  of  the  amount  of  shot  necessary  to  remove  the  cut- 
tings without  displacing  the  shot;  and  of  the  pressure  to  exert 
upon  the  bit  to  obtain  the  most  effective  cutting.  The  most 
serious  difficulty  is  due  to  crevices  in  the  rock  in  which  the  shot 
may  be  lost,  requiring  either  some  means  of  artificially  sealing 
the  openings,  feeding  the  shot  slowly  but  continuously  by  an 
expert  operator,  or  substituting  a  toothed  bit  to  drill  past  the 
crevice.  Some  machines  are  arranged  to  imbed  the  shot  in  the 
bit  by  churning  instead  of  direct  pressure. 

In  another  type  of  drill  without  the  use  of  diamonds,  steel 
bits  are  used  with  different  forms  of  teeth,  and  also  operated 
by  rotation.  One  of  these  known  as  the  Davis  cutter  has 
long,  tempered  steel  teeth  with  angles  from  30  to  35  degrees, 
while  between  them  are  vertical  grooves  on  the  outer  surface 
of  the  bit.  Instead  of  grinding  with  a  uniform  motion  the  long 
teeth  chip  away  the  rock  by  an  action  closely  resembling  that 
of  a  hammer  and  chisel.  This  cutter  is  used  for  the  softer 
rocks,  as  well  as  for  other  material  overlying  the  rock,  instead 
of  a  chopping  bit. 

An  excellent  article  by  ROBERT  RIDGEWAY  on  boring  methods 
and  machines,  difficulties  encountered  and  results  of  explora- 
tions in  various  mixtures  of  glacial  materials  as  well  as  rock,  is 
entitled  Sub-surface  Investigation  on  the  Catskill  Aqueduct, 
Board  of  Water  Supply,  in  Engineering  Record,  vol.  57,  pages 
522  and  557,  April  18  and  25,  1908.  See  also  Chap.  IV  on 
Borings  and  Sub-surface  Investigations  in  a  volume  on  The 
Catskill  Water  Supply  of  New  York  City  by  LAZARUS  WHITE, 
New  York,  1913. 


ART.  177 


NEED  OF  SUB-SURFACE  EXPLORATION 


529 


ART.  177.     NEED  OF  SUB -SURFACE  EXPLORATIONS 


It  is  as  essential  to  the  proper  design  of  foundations  to 
determine  accurately  the  local  conditions  under  the  surface  of 
the  ground  or  below  the  bed  of  a  stream  as  to  observe  the  con- 
trolling conditions  of  the  stream  itself,  or  to  know  the  character 
of  the  superstructure  and  the  magnitude  and  direction  of  all 
the  external  forces  acting  upon  the  substructure.  To  discover 
the  character  of  the  underlying  strata  and  to  find  their  respect- 
ive depths  below  high  and  low  water  in  the  case  of  a  bridge,  or 
below  the  surface  or  the  level  of  ground  water  in  the  case  of  a 
building,  it  is  necessary  to  make  excavations,  or  borings,  and 
in  some  instances  to  drive  test  piles.  In  many  locations  con- 
ditions vary  greatly  within  short  distances. 

Adequate  exploration  is  often  omitted  because  of  the  labor, 
time  and  cost.  The  cost  of  exploration,  however,  is  frequently 
less  than  that  otherwise  required  merely  to  revise  the  plans 
of  the  structures  involved,  without  considering  the  unnecessary 
cost  of  the  structures  due  to  lack  of  information.  There  are 
abundant  examples  to  prove  that  where  adequate  exploration 
is  omitted,  it  may  result  in  the  loss  of  the  structure,  or  in 
greatly  increased  cost.  In  one  instance  a  bridge  pier  was  built 
upon  a  surface  of  hard-pan  in  the  river  bottom.  No  examina- 
tion was  made  on  account  of  the  swift  current  which  had  a  ve- 
locity of  5  miles  per  hour.  Without  warning  the  pier  sank  out 
of  sight  causing  the  loss  of  the  two  adjacent  spans  of  the  bridge, 
and  of  a  number  of  human  lives.  Upon  making  an  investiga- 
tion afterward  it  was  found  that  the  hard-pan  was  only  a  thin 
stratum  overlying  a  deep  layer  of  soft  clay.  In  another  ex- 
ample a  bridge  abutment  which  was  founded  on  6o-foot  timber 
piles  settled  slowly  until  it  reached  a  maximum  of  3  feet,  after 
an  attempt  to  stop  it  by  means  of  additional  piles  around  the 
outside.  Exploration  proved  the  settlement  to  be  due  to  a 
lo-foot  layer  of  peat  35  feet  below  the  surface,  which  was  flow- 
ing apparently  under  the  superimposed  load.  This  experi- 
ence emphasizes  the  statement  made  in  Art.  36  that  test  piles 
alone  may  be  insufficient.  Experience  has  also  shown  that  the 

34 


530  EXPLORATIONS  AND   UNIT   LOADS  CHAP.  XVII 

cost  of  exploration  may  frequently  save  much  larger  sums  in 
the  annual  cost  of  maintenance  of  structures  like  pile  trestle 
bridges.  In  a  certain  project  the  chief  engineer  estimated  that 
$100000  was  saved  in  the  cost  of  construction  by  a  thorough 
preliminary  exploration  of  the  ground. 

Another  important  reason  why  adequate  explorations  should 
be  made  is  that  the  owner  ought  to  assume  full  responsibility 
for  the  local  conditions  and  that  the  contractor  should  not  be 
obliged  to  gamble  on  uncertainties  relating  thereto.  The  con- 
tractor should  be  asked  to  bid  on  guaranteed  local  conditions, 
with  an  increase  or  reduction  in  price  for  variations  from  these 
that  may  be  discovered  later.  Occasionally  inadequate  explora- 
tions may  be  made  which  are  equally  unfair  to  the  contractor. 
For  example,  only  four  borings  were  made  on  a  city  block  to  be 
covered  by  an  important  building,  dne  at  each  corner;  but  it 
was  distinctly  stated  that  these  borings  were  furnished  as  general 
and  not  as  specific  information  to  the  contractor  and  that  he 
must  assume  all  chances  as  to  the  sub-surface  formations.  The 
contract  price  for  the  foundations  alone  was  $208453.00. 

An  engineer  of  large  experience  made  the  following  statement 
in  1910,  based  upon  his  own  practice  and  his  observations  of 
ordinary  conditions: 

"I  consider  it  very  important  and  the  expenditure  well  warranted  to 
first  determine  definitely  by  test  borings  or  drilling  what  the  actual  depth 
and  character  of  the  foundation  is  before  any  detailed  plans  are  prepared. 
Such  determinations  enable  the  designer  to  design  the  structure  as  it 
should  be  built  to  meet  the  conditions,  assuming  that  the  test  borings  or 
drillings  have  been  properly  made,  and  such  an  order  of  procedure  saves 
much  time  in  the  designing  room  by  eliminating  numerous  changes  in 
plans  where  unexpected  conditions  arise  when  the  foundations  are  being 
excavated,  and  which  is  frequently  the  case.  In  nearly  all  cases  there  is 
a  hurry  to  start  the  foundation  masonry  and  frequently  plans  cannot  be, 
or  are  not,  properly  modified  to  suit  the  conditions  and  meet  the  require- 
ments of  economy.  Furthermore,  with  a  proper  knowledge  of  the  founda- 
tions the  contractor  is  placed  in  possession  of  definite  information,  and 
with  the  plans  properly  designed  once  and  for  all,  with  possibly  some  minor 
modifications,  the  result  is  a  large  economy  to  the  company  paying  for  the 
work,  and  which  also  eliminates  questions  of  extra  prices  and  frequently 
some  arguments  over  changed  conditions  affecting  unit  prices." 


ART.  178  TEST  FOR  BEARING  CAPACITY  531 

In  general,  two  sets  of  borings  should  be  made  for  an  impor- 
tant bridge  crossing.  In  the  first  set  a  number  of  borings  are 
located  on  the  center  line  of  the  proposed  location,  to  determine 
whether  the  site  furnishes  favorable  conditions;  and  if  so  to 
make  an  approximate  estimate  of  the  most  economical  location 
of  the  piers  and  the  length  of  spans.  Sometimes  government 
regulations  for  navigable  streams  or  the  influence  of  ice  or 
flood  conditions  must  also  be  considered.  After  the  piers  are 
located  tentatively  additional  borings  should  be  made  at  the 
site  of  each  pier.  At  least  four  borings,  or  one  at  each  corner, 
are  necessary,  and  several  intermediate  ones  may  be  required 
unless  the  adjacent  indications  are  nearly  the  same. 

ART.  178.     TESTS  FOR  BEARING  CAPACITY 

After  an  exploration  has  been  made  of  the  different  strata  a 
test  should  be  made  at  the  surface  on  which  the  foundation  is  to 
rest  to  determine  the  bearing  capacity  of  the  ground.  Fig.  1780 
shows  the  appliances  often  used  for  this  purpose,  the  hard-pan 
being  tested  at  the  base  of  a  pier  to  be  built  in  an  open  well. 
The  surface  is  scraped  to  a  level  plane  by  means  of  a  straight- 
edge. The  platform  is  loaded  with  blocks  of  cast  iron  or  other 
weights,  and  is  transferred  to  the  bearing  plate  at  the  foot  of 
the  post.  The  platform  is  held  in  proper  position  by  wedges 
loosely  placed  against  the  sheeting,  and  the  settlement  is  meas- 
ured by  taking  readings  on  the  steel  tape  at  the  top  of  the  shaft. 
In  one  example  of  such  a  test,  a  load  of  24200  pounds  per  square 
foot  produced  a  settlement  of  f\  inch  in  44  hours.  The  working 
load  adopted  was  13  300  pounds  per  square  foot. 

When  the  platform  is  placed  above  the  natural  surface  it 
may  be  braced  conveniently  by  extending  the  post  above  the 
height  to  be  occupied  by  the  loading,  and  into  a  loosely  fitting 
collar  which  is  held  in  position  by  four  inclined  shores;  or  four 
vertical  timbers  supported  by  shores  may  be  placed  so  as  to 
correspond  to  the  four  sheeting  planks  which  take  bearing  from 
the  wedges  in  Fig.  1780. 

To  determine  the  bearing  power  of  the  sand  on  which  some 


532 


EXPLORATIONS  AND  UNIT   LOADS 


CHAP.  XVII 


of  the  pneumatic  caissons  under  the  Municipal  Building  in  New 
York  City  were  to  be  founded,  a  1 6-inch  casing  was  driven, 

and  cleaned  out  by  means  of 
a  sand  pump.  Inside  of  the 
casing  was  placed  a  lo-inch 
pipe  having  a  bearing  disk 
14  inches  in  diameter  at- 
tached at  the  bottom  and  a 
balanced  platform  at  the  top 
to  receive  the  load.  Three 
tests  were  made  at  different 
depths.  At  a  depth  of  77 
feet  below  the  curb  loads  of 
15,  22.5  and  28  tons  per 
square  foot  produced  settle- 
ments of  |J,  i  If  and  2  If 
inches  respectively.  Later 
one  of  the  circular  caissons 
was  tested.  Its  base  had  an 
area  of  90.8  square  feet  and 
was  72  feet  below  the  curb. 
The  load  was  applied  by  in- 
crements of  i  ton  per  square 
foot  every  24  hours.  A  load 
of  6  tons  per  square  foot, 
which  was  that  used  in  de- 
signing the  caissons,  caused 
a  settlement  of  J  inch  with- 
out further  increase  during  a 
rest  of  six  days.  After  the 
load  was  increased  to  10  tons 


Hardpan 
FIG.   i;8a. 


per    square    foot    the    total 
settlement  was  if  inch  with- 
out further  increase. 

The  following  extract  is  made  from  the  regulations  (1912) 
of  the  Building  Department  of  the  Borough  of_Manhattan: 


ART.  178  TESTS  FOR  BEARING  CAPACITY  533 

"The  soil  shall  be  tested  in  one  or  more  places  as  the  conditions  may 
determine  or  warrant,  at  the  level  at  which  it  is  proposed  to  place  the 
bottom  of  the  foundations  of  the  structure.  Each  test  shall  be  made  so 
as  to  load  the  soil  over  an  area  of  not  less  than  4  square  feet  in  any  one  place. 
The  accepted  safe  load  shall  not  exceed  two-thirds  of  the  final  test  load. 
The  loading  of  the  soil  shall  proceed  as  follows:  (a)  The  load  per  square 
foot  which  it  is  proper  to  impose  upon  the  soil  shall  be  first  applied  and 
allowed  to  remain  for  at  least  48  hours  undisturbed,  measurements  or 
readings  being  taken  once  each  24  hours  or  oftener  to  determine  the  settle- 
ment, if  any.  (b)  After  the  expiration  of  the  48  hours  the  additional  50 
percent  excess  load  shall  be  applied  and  the  total  load  allowed  to  remain 
undisturbed  for  a  period  of  at  least  six  days,  careful  measurements  and 
readings  being  taken  once  in  24  hours,  or  oftener,  in  order  to  determine 
the  settlement.  The  test  shall  not  be  considered  satisfactory  or  the 
result  acceptable  unless  the  proposed  safe  load  shows  no  appreciable 
settlement  for  at  least  two  days  and  the  total  test  load  shows  no  settlement 
for  at  least  four  days." 


The  loaded  area  has  most  frequently  been  taken  at  i  square 
foot,  but  it  is  better  to  take  a  larger  area  like  that  specified  in 
the  preceding  paragraph  and  to  subject  it  to  a  load  not  exceeding 
twice  that  of  the  proposed  working  load  than  to  overload  a 
much  smaller  area.  To  get  the  best  results  it  is  important  to 
make  the  test  on  a  surface  as  near  the  elevation  of  the  proposed 
base  of  the  foundation  as  possible,  not  at  the  surface  of  the 
ground,  and  with  as  little  clearance  as  possible  between  the 
bearing  disk  or  plate  and  the  sides  of  the  excavation  or  casing. 
It  is  also  desirable  to  know  whether  any  elasticity  exists  in  the 
ground,  and  for  this  purpose  the  reduction  in  settlement  should 
be  measured  as  the  load  is  taken  off  in  parts  with  short  intervals 
of  rest  between.  The  unloading  may  be  done  more  rapidly 
than  the  loading.  Tests  on  beds  of  clay  should  extend  over 
longer  time  intervals  depending  upon  their  character. 

An  excellent  graphic  representation  of  the  phenomena  of 
tests  for  bearing  power  consists  in  laying  off  the  time  intervals 
as  abscissas,  the  loads  per  square  foot  as  positive  ordinates, 
and  the  settlements  as  negative  ordinates.  The  curve  of 
settlement  below  the  axis  can  thus  be  compared  directly  with 
the  stepped  load  line  above  the  axis,  showing  the  effect  of  both 


• 


534  EXPLORATIONS   AND  UNIT  LOADS  CHAP.  XVII 

increase  in  load  and  of  intervals  of  rest  after  the  successive 
increments  of  load. 


ART.  179.     VALUES  OF  BEARING  CAPACITY 

No  definite  values  can  be  given  in  general  to  the  safe  loads 
on  foundation  beds  since  it  is  impossible  to  classify  accurately 
the  various  kinds  of  earth.  Unless  the  bearing  capacity  of  the 
material  at  a  given  site  is  already  known  it  should  be  determined 
by  direct  experiment.  Too  little  attention  has  been  given  to 
this  subject  and  but  small  additions  have  been  made  in  recent 
years  to  any  real  knowledge  of  the  material  on  which  the 
foundations  of  structures  rest.  For  preliminary  estimates  and 
some  other  purposes,  limiting  values  of  bearing  capacity  may  be 
employed  for  several  classes  of  material. 

In  his  General  Specifications  for  Structural  Work  of  Buildings, 
C.  C.  SCHNEIDER  recommends  that  the  pressures  on  foundations 
are  not  to  exceed  the  following  values  in  tons  per  square  foot: 
Soft  clay,  i;  ordinary  clay  and  dry  sand  mixed  with  clay,  2; 
dry  sand  and  dry  clay,  3;  hard  clay  and  firm,  coarse  sand,  4; 
firm,  coarse  sand  and  gravel,  6.  Other  experienced  engineers 
have  characterized  these  values  as  needlessly  conservative,  but 
it  was  claimed  in  reply  that  conservative  values  were  adopted 
because  the  effect  of  settlement  in  the  foundation  of  a  building 
is  more  injurious  than  in  a  bridge  pier.  The  same  specifications 
also  contain  a  table  giving  the  bearing  capacity  for  different 
kinds  of  ground  as  prescribed  in  the  building  codes  of  a  number 
of  American  cities. 

The  Building  Code  recommended  by  the  National  Board 
of  Fire  Underwriters  gives  the  following  limiting  values,  also 
expressed  in  tons  per  square  foot:  Soft  clay,  i;  clay  and  sand 
together,  wet  and  springy,  2;  loam,  clay  and  fine  sand,  firm 
and  dry,  3 ;  very  firm,  coarse  sand,  stiff  gravel  or  hard  clay,  4. 

In  H.  B.  SEAMAN'S  Specifications  for  Bridges  and  Subways 
the  allowable  static  pressures  are  given  as  follows,  in  tons  per 
square  foot:  Silt,  i;  moist  clay,  2;  clean  sand  or  dry  clay,  4; 
coarse  sand  or  gravel,  6;  hard-pan  or  compacted  gravel,  10; 


ART.  179  VALUES  OF  BEARING  CAPACITY  535 

sound  ledge  rock,  60.  It  is  stated,  however,  that  these  pres- 
sures are  for  the  most  favorable  conditions,  and  that  for  ques- 
tionable material  they  should  be  reduced  50  percent.  In 
deep  foundations,  friction  and  buoyancy  may  be  allowed  for 
in  computation. 

The  following  paragraph  is  quoted  from  J.  E.  GREINER'S 
General  Specifications  for  Bridges,  Part  III: 

"85.  When  foundations  are  subjected  to  the  loads  and  forces  specified 
in  paragraph  84,  the  maximum  permissible  pressure  per  square  foot  on 
any  part  of  the  surface  of  the  supporting  strata,  when  in  thick  beds,  shall 
be  as  follows,  but  it  is  advisable  to  use  a  considerably  less  pressure  unless 
absolutely  certain  as  to  the  character  of  the  bottom.  Firm  rock,  30; 
dry  coarse  gravel  and  sand,  well  cemented,  5;  hard  dry  compact  sand,  4; 
hard  dry  clay,  3  tons." 

The  following  allowable  loads,  expressed  in  tons  per  square 
foot,  were  adopted  Oct.  n,  1905,  by  the  Harriman  Lines: 
Alluvial,  adobe,  soil,  0.5;  clean,  dry  sand,  2;  compact  sand, 
cemented,  4;  gravel  and  sand,  cemented,  8;  moist,  soft  clay,  i; 
dry  clay  in  thick  beds,  4;  soft  bedrock,  5;  hard  bedrock,  20; 
hardest  bedrock  with  no  seams,  200. 

The  most  elaborate  collection  of  data  on  unit  pressures 
adopted  for  stable  structures  on  the  material  upon  which  they 
are  founded  is  contained  in  a  volume  entitled  Allowable  Pres- 
sures on  Deep  Foundations,  by  ELMER  L.  CORTHELL.  The 
data  relate  to  178  works,  and  an  analysis  of  some  of  them  gives 
the  following  results: 

Examples  Material  Range  of  pressure,  Ibs.   Average,  Ibs. 

10  Fine  sand  4  500-11  600  9  ooo 

33          Coarse  sand  and  gravel        4  800-15  500  10  200 

10  Sand  and  clay  5  000-17  ooo  9  800 

7  Alluvium  and  silt  3  000-12  400  5  800  - 

16  Hard  clay  4  000-16  ooo  10  160 

5  Hard-pan  6000-24000  17400 

"  These  cases  show  no  settlement.  The  range  is  considerable 
and  no  doubt  in  the  case  of  the  minimum  pressure  a  much  larger 
weight  could  have  been  imposed  on  the  material  without  pro- 
ducing settlement.  For  a  safe  rule,  therefore,  the  average  is 


EXPLORATIONS   AND   UNIT   LOADS  CHAP.  XVII 

low  and  a  safe  pressure  upon  the  material  would  lie  somewhere 
between  the  average  and  the  maximum  pressure."  The  same 
volume  contains  the  pressure  for  instances  in  which  notable 
settlement  took  place,  as  well  as  values  of  frictional  resistance 
for  cylinder  and  masonry  piers. 

The  bearing  capacity  of  the  ground  depends  not  only  upon 
its  character  or  composition  but  also  on  the  amount  of  water 
which  it  contains  or  is  liable  to  receive,  and  the  degree  to  which 
it  is  confined  to  its  location.  Sand  can  sustain  very  heavy 
loads  with  but  slight  or  negligible  compression.  When  it 
directly  overlays  rock  or  some  other  thick  stratum  of  hard 
material  and  is  securely  confined,  or  is  artificially  protected 
against  the  possibility  of  lateral  displacement,  it  forms  a  satis- 
factory foundation  bed  and  will  safely  carry  heavy  loads. 

The  supporting  power  of  clay  is  very  variable  and  depends 
in  a  large  measure  upon  its  variety  and  upon  its  degree  of  satu- 
ration with  moisture.  The  clays  vary  considerably  in  their 
chemical  constituents,  which  in  turn  affect  the  amount  of  mois- 
ture which  they  can  absorb.  Certain  deposits  are  known  to  be 
compact  and  hard  and  have  a  high  supporting  power,  while 
others  are  plastic  and  easily  compressed.  The  chief  character- 
istic which  renders  clay  more  or  less  unstable  as  a  foundation 
material  is  its  property  of  retaining  water  which  is  once  ad- 
mitted, and  its  tendency  to  soften  gradually  as  the  amount  of 
water  increases.  In  plastic  clay  and  other  soft  material  the 
depth  of  foundation  should  enter  as  a  factor  in  determining  the 
allowable  pressure.  In  other  words,  the  so-called  buoyancy  of 
the  foundation  material  is  a  function  of  the  depth  of  'displace- 
ment' of  the  building  or  other  structure.  The  point  of  bearing 
must  be  carried  below  the  possibility  of  upward  reaction  along- 
side. This  principle  has  sometimes  found  expression  in  a 
practical  rule  that  "in  compressible  ground  the  depth  of  a 
foundation  ought  not  to  be  less  than  one-fourth  of  the  intended 
height  of  the  building  above  ground;  that  is,  for  a  shaft  of  200 
feet,  the  foundation  should  be  made  secure  to  a  depth  of  50  feet 
by  piling,  or  by  well-sinking  and  concrete.  Masses  of  concrete, 
brick,  or  stone,  placed  upon  a  compressible  substratum,  how- 


ART.  179         VALUES  OF  BEARING  CAPACITY          »  537 

ever  cramped  or  bound,  may  prove  unsafe.  Solidity  for  a 
considerable  depth  alone  can  be  relied  upon.  Mere  enlarge- 
ment of  a  base  may  not  in  itself  be  sufficient."  It  must  also 
be  remembered  that  large  areas  of  compressible  ground  will  not 
continuously  support  as  large  a  unit  load  as  a  smaller  area  for 
a  short  time. 

When  clay  is  mixed  with  other  materials,  like  coarse  sand  and 
gravel,  its  supporting  power  is  considerably  increased,  being 
greater  in  proportion  as  the  other  materials  are  in  excess  up  to 
the  point  of  forming  a  cemented  mass,  in  which  the  clay  is 
just  sufficient  in  quantity  to  act  as  a  cement  in  binding  the 
other  materials  together.  In  this  condition  the  clay  is  often 
found  in  an  indurated  state,  and  the  hardness  of  the  mixture, 
commonly 'called  hard-pan,  is  proverbial. 


CHAPTER  XVIII 
PNEUMATIC  CAISSON  PRACTICE1 

ART.  180.     HISTORICAL  NOTES 

In  1852  an  attempt  was  made  in  the  Pedee  River  in  North 
Carolina  to  use  the  ingenious  vacuum  method,  invented  by 
POTTS,  to  place  the  foundations  for  a  bridge.  His  plan  con- 
sisted in  exhausting  the  air  from  cylinders  6  feet  in  diameter, 
thereby  causing  the  atmosphere  to  exert  a  pressure  of  14.7 
pounds  per  square  inch,  or  a  total  pressure  of  about  30  tons 
which  it  was  thought  would  force  each  cylinder  through  a 
depth  of  25  feet  of  sand.  Unfortunately,  the  attempt  proved 
unsuccessful,  since  no  allowance  had  been  made  for  the  presence 
of  logs  which  were  encountered  under  the  cutting  edge. 

Accordingly,  the  opposite  method  was  tried,  or  that  of  pump- 
ing additional  air  into  the  cylinders,  thus  introducing  in  America 
what  was  designated  as  the  plenum  pneumatic  method.  By 
this  method  the  air  is  compressed  sufficiently  to  balance  the 
water  pressure,  thus  keeping  the  water  out  of  the  working 
chamber.  As  a  cubic  foot  of  fresh  water  weighs  about  62^ 
pounds,  the  pressure  per  square  inch  at  a  depth  of  i  foot  is 
0.434  pounds  and  at  a  depth  of  100  feet,  43.4  pounds. 

The  second  set  of  caissons  to  be  sunk  in  America  were  those 
of  the  Third  Avenue  bridge  over  Harlem  River,  New  York, 
about  1860,  the  third  being  those  for  the  famous  steel  arch 
bridge  at  St.  Louis  begun  in  1868.  The  earliest  patent  for 
a  compressed-air  shaft  was  granted  to  THOMAS  COCHRANE  in 
1830,  while  the  first  application  was  made  in  the  river  Seine,  at 
Loire,  by  M.  TRIGER  in  1839.  Compressed  air  had  been  used 
in  diving  bells,  however,  for  many  centuries,  although  the  first 

1  By  T.  KENNARD  THOMSON,  C.  E.,  D.  Sc.,  Consulting  Engineer,  50  Church 
St.,  New  York  City. 

538 


ART.  181  RESULTS   OF   EVOLUTION  539 

record  of  using  a  pump  to  compress  the  air  in  a  diving  bell  is  in 
1778  by  SMEATON,  a  noted  English  engineer,  for  repairing  the 
foundations  of  a  bridge  over  the  river  Tyne,  at  Hexham. 


ART.  181.     RESULTS  OF  EVOLUTION 

The  first  and  second  sets  of  caissons  referred  to  in  Art.  180 
were  iron  cylinders  only  4  to  6  feet  in  diameter.  The  first  large 
caissons  were  built  for  the  deep  foundations  of  the  Eads  bridge 
at  St.  Louis  and  the  Brooklyn  bridge  in  New  York.  They  were 
of  very  massive  timber  construction  on  account  of  the  stone 
masonry  being  placed  directly  upon  the  deck.  The  heavy 
roof  or  deck  was  also  used  in  the  early  days  of  concrete  by  some 
engineers,  but  in  the  decade  following  1880,  the  thickness  was 
reduced  to  less  than  3  feet  for  bridge  piers  in  some  of  the  large 
rivers.  In  the  Hartford  stone  arch  bridge,  the  largest  caisson 
was  46  by  131  feet  in  size  and  had  a  timber  deck  only  4  feet 
thick.  As  this  caisson  had  no  bulkheads  or  diaphragms,  it 
contained  the  largest  undivided  air-chamber  ever  used.  Mass- 
ive framed  timber  cribs  with  solid  walls  and  heavy  bracing  were 
also  used  above  the  caisson  deck,  but  the  walls  were  reduced  in 
time  to  3-inch  planking  with  sufficient  timber  bracing  to  resist 
the  water  pressure  and  possible  bumps  from  boats,  etc. 

The  first  building  ever  founded  on  pneumatic  caissons  was 
the  Manhattan  Life  building  at  66  Broadway,  New  York,  in 
1893.  The  caissons  were  of  heavy  steel  construction,  about 
9  feet  high  with  a  7-foot  working  chamber.  It  was  intended  to 
build  the  brick  piers  directly  on  the  caissons  as  they  sank,  but 
the  friction  of  the  ground  against  the  brick  wall  was  too  great 
for  the  green  mortar  and  forced  open  the  joints  between  the 
brick.  This  method  was  then  replaced  by  building  steel 
cofferdams  above  the  caisson  and  filling  them  with  concrete. 
The  steel  in  turn  was  supplanted  by  wood. 

Caissons  and  cofferdams  built  of  steel  with  rectangular 
horizontal  sections  were  used  for  many  years,  but  have  been 
abandoned  in  America  while  those  with  circular  sections  are 
restricted  to  small  diameters.  Except  for  the  small  sizes,  it  is . 


540  PNEUMATIC   CAISSON   PRACTICE  CHAP.  XVIII 

always  cheaper  to  use  wood  and  concrete;  and  in  many  cases  it 
is  cheaper  to  use  wood  only  for  forms  when  all  the  concrete  can 
be  placed  before  sinking  starts,  and  which  has  often  been  done 
successfully  up  to  heights  a  little  over  30  feet  above  the  cutting 
edge.  This  method  is  not  economical,  however,  when  the 
depth  of  sinking  is  so  large  as  to  require  two  or  three  'build-ups' 
of  concrete  during  which  the  sinking  must  be  interrupted. 

To  stop  sinking  temporarily  is  bad  since  it  requires  continual 
pumping  of  air  during  the  interval,  thus  increasing  the  overhead 
charges,  and  also  allows  the  ground  to  cake  against  the  sides, 
thus  greatly  increasing  the  friction.  In  one  example,  the  mov- 
able derrick  was  shifted  to  another  caisson  instead  of  waiting 
several  days  for  the  'build-up,'  as  the  adding  of  concrete  is 
called,  and  it  was  60  days  before  sinking  was  resumed  on  this 
caisson.  During  this  period  compressed  air  was  pumped  into 
the  working  chamber  to  keep  the  ground  from  caving  in, 
although  it  would  have  been  cheaper  to  flood  the  caisson  for  that 
purpose.  It  is  much  cheaper  in  such  cases  to  use  a  cofferdam 
of  2-inch  plank  and  to  work  continuously  until  the  penetra- 
tion is  completed. 

To  sum  up  the  results  of  evolution,  it  is  found  to  be  the  best 
practice  to  use  steel  for  small  circular  caissons,  say  from  30 
inches  to  6  feet  in  diameter;  in  larger  sizes  to  use  mass  concrete 
with  2-inch  timber  sides,  with  reinforcement  around  the  shafts, 
working  chamber  and  sides,  where  it  is  necessary  to  keep  joints 
from  opening.  It  is  believed  to  be  better  to  leave  on  the  thin 
timber  sides,  since  it  avoids  unnecessary  delays  in  sinking, 
reduces  the  skin  friction  as  well  as  the  liability  of  rupturing  the 
concrete  due  to  the  friction,  and  makes  it  easier  to  keep  the 
caissons  plumb  and  in  position. 

Caissons  with  a  timber  roof  and  sides  for  the  working  chamber 
and  with  timber  cofferdam  on  top  are  economical  for  only  deep 
sinking  in  harbors  or  rivers,  where  buoyancy  is  an  advantage. 
The  writer  has  sunk  caissons  in  water  60  feet  deep  where  the 
cutting  edge  had  to  penetrate  30  feet  below  the  bottom.  The 
top  of  the  concrete  had  to  be  kept  about  25  feet  below  the  water 
surface  in  the  river,  requiring  great  care  with  the  bracing  of  the 


ART.  182  CONSTRUCTION  OF  CAISSONS  541 

timber  cofferdam  and  to  guard  against  concrete  buckets  knock- 
ing out  braces,  as  well  as  injury  from  passing  barges,  derrick 
boats,  etc.  If  no  timber  had  been  used  in  constructing  the 
caisson,  the  distance  from  the  water  surface  to  the  concrete 
being  deposited  would  have  been  much  greater. 

ART.  182.     CONSTRUCTION  OF  CAISSONS 

For  constructing  caissons  from  30  to  36  inches  in  diameter, 
such  as  are  used  chiefly  for  underpinning  purposes,  cast  iron  is 
preferable,  with  a  thickness  of  ij  to  ^  inches.  The  sections 
should  be  about  5  feet  long  with  substantial  flanges  to  bolt 
them  together,  shorter  sections  being  ordered  to  make  up  the 
requisite  total  length,  which  varies  in  each  case.  See  illustra- 
tions in  an  article  on  Foundations  of  the  New  Mutual  Life 
Insurance  Building,  New  York  City,  in  Engineering  News,  vol. 
45,  page  221,  March  28,  1901.  Steel  plates  f  inch  thick  have 
been  used  but  in  some  cases  were  badly  twisted  or  warped  while 
being  jacked  down,  thus  greatly  reducing  if  not  destroying  the 
value  of  the  cylinders  as  columns.  Cast  iron  is  much  less 
liable  to  rust  than  steel. 

When  caissons  are  sunk  in  the  open  for  new  buildings,  it 
rarely  pays  to  use  a  smaller  diameter  than  6  feet;  the  working 
chamber  then  consists  of  a  steel  shell  about  f  inc  hthick,  with 
a  steel-angle  ring  above  the  cutting  edge  and  one  or  two  more 
rings  of  say  3|X3JX^-inch  angles  between  the  cutting  edge 
and  the  deck.  If  the  steel  cofferdam  above  a  caisson  of  this 
diameter  is  omitted  and  removable  forms  used,  the  ring  of  con- 
crete between  the  inside  shaft  and  outside  surface  is  only  from 
i  to  ij  feet  in  thickness,  and  unless  the  concrete  is  heavily 
reinforced,  both  vertically  and  horizontally,  the  concrete  is  sure 
to  crack  as  has  often  been  proved  by  experience.  The  size 
arid  spacing  of  the  reinforcing  bars  depends  on  the  depth  of 
penetration,  and  in  these  circular  caissons,  6  feet  or  over  in  di- 
ameter, it  is  often  more  economical  to  use  wooden  sides  from  the 
cutting  edge  to  the  top. 

In  the  larger  caissons,  whether  of  wood  or  concrete,  the  first 


542  PNEUMATIC   CAISSON  PRACTICE  CHAP.  XVIII 

detail  of  construction,  and  on  which  there  is  still  the  widest 
difference  of  opinion,  is  the  cutting  edge.  Naturally,  every 
one  wants  the  bottom  of  the  caisson  to  be  as  thin  as  possible, 
so  that  the  sand  hogs  can  remove  the  material  under  the  cutting 
edge  with  the  least  difficulty.  Most  superintendents  demand 
a  'knife  cutting  edge/  which  is  a  mistaken  policy,  for  in  fine 
sand  where  such  a  knife  edge  works  like  a  charm,  it  is  not 
needed,  whereas  in  other  material  where  it  seems  to  be  needed 
it  cannot  be  made  strong  enough  to  stand  the  terrific  pressure. 
It  is  sure  to  be  buckled  and  then  becomes  worse  than  no  cut- 
ting edge  at  all,  often  causing  considerable  delay,  while  it  is 
being  removed. 

The  best  form  of  cutting  edge  for  either  timber  or  concrete 
caissons  consists  of  an  8-inch  channel  laid  flat  with  its  back 
down,  or  a  1 2-inch  oak  block  sized  down  to  8  inches  on  the 
bottom.  The  8-inch  channel  cutting  edge  was  first  designed 
by  the  writer  for  Arthur  McMullen  &  Co.,  in  1901,  and 
it  has  been  used  by  them  frequently.  It  is  the  most 
economical  form. 

The  side  walls  of  the  working  chamber  require  great  care  and 
judgment  in  their  design.  Theoretically,  if  the  caisson  is 
plumb,  and  the  air  pressure  just  balances  the  outside  pressure 
there  is  no  pressure  on  the  sides  except  that  due  to  the  load 
on  the  top,  including  the  weight  of  concrete  placed.  But  cais- 
sons are  very  rarely  absolutely  plumb,  and  they  often  get  badly 
warped  as  well  as  inclined,  due  to  more  obstruction  on  one 
side  than  on  the  other,  causing  the  sides  frequently  to  buckle, 
sometimes  to  collapse,  or  to  break  away  from  the  roof.  In 
one  instance,  where  the  last  kind  of  accident  occurred,  the 
cutting  edge  was  in  sand  about  20  feet  above  rock,  and  had  to 
be  left  there,  the  balance  of  the  excavation  being  made  by  a 
vertical  tunnel  method.  In  another  example,  the  side  walls  of 
the  working  chamber  made  of  f  -  and  ^-inch  steel  plates,  braced 
firmly  every  i\  feet,  have  been  observed  to  buckle  at  least  2 
inches  under  the  outside  pressure. 

Timber  side  walls  are  most  readily  braced  and  repaired,  but 
must  be  firmly  attached  to  the  structure  above  to  prevent 


ART.  182  CONSTRUCTION  OF  CAISSONS  543 

breaking  away.  In  another  instance,  a  reinforced-concrete 
caisson  landed  hard  on  one  side,  and  in  consequence  the  steel 
rods  from  the  cutting  edge  up  were  badly  buckled,  forcing  the 
concrete  side  walls  into  the  working  chamber,  leaving  the  out- 
side timber  bare,  which  fortunately  had  been  left  in  place. 
Curiously,  the  thick  reinforced-concrete  wall  was  destroyed, 
while  the  3 -inch  plank  remained. 

In  small  caissons  the  cutting  edge  and  sides  should  be  made 
strong  enough  to  withstand  the  pressure  without  cross  bracing, 
but  in  large  caissons  it  is  customary  to  use  substantial  struts 
every  10  or  15  feet,  and  most  designers  use  solid  timber  bulk- 
heads in  long  or  wide  caissons,  making  an  air  chamber  about 
20  feet  wide.  However,  as  every  bulkhead  makes  two  more 
cutting  edges  to  work  under,  and  since  this  part  of  the  ex- 
cavation is  the  most  expensive,  the  writer  has  preferred  to 
omit  the  bulkheads  and  has  done  so  successfully  up  to  a 
width  of  46  feet  and  a  length  of  131  feet,  at  Hartford,  Conn. 
The  size  and  spacing  of  this  bracing  must  be  governed 
by  experience.  The  caissons  at  Hartford  are  typical  of  others 
used  successfully  at  Pittsburgh,  Mingo  Junction,  Havre  de 
Grace,  and  Pierre. 

The  earliest  wooden  caissons  had  much  heavier  wooden 
decks  than  were  needed  to  act  as  supports  for  the  stone  ma- 
sonry. Steel  caissons  also  had  heavy  beam  deck  construction 
even  when  concrete  was  supported.  It  was  long  thought  neces- 
sary to  have  a  timber  or  steel  deck  to  secure  an  air-tight  job, 
but  experience  has  shown  that  by  first  placing  a  layer  of  mortar, 
it  is  easier  to  secure  air- tightness  with  concrete  than  with  wood 
or  steel.  Upon  reflection,  it  was  seen  that  under  concrete  a 
deck  of  timber  or  steel  was  needed  only  as  a  temporary  form, 
except  when  the  concrete  was  shallow  and  then  it  could  be 
reinforced. 

There  are  three  good  reasons  for  omitting  the  permanent 
wooden  deck :  First,  it  is  more  compressible  than  concrete  and 
is  liable  to  loads  sufficient  to  compress  it;  second,  concrete  is 
cheaper  than  wood;  and  third,  danger  of  injury  from  the  teredo 
wherever  it  exists.  The  old  theory  that  the  teredo  will  only 


544  PNEUMATIC   CAISSON  PRACTICE  CHAP.  XVIII 

start  work  near  the  water  surface  is  erroneous  according  to 
the  observations  of  the  writer  who  examined  piles  driven  two 
years  previously  for  a  bridge  at  Fall  River,  Mass.,  and  which 
were  cut  off  40  or  50  feet  below  the  surface,  and  carried  a 
timber  grillage  4  feet  thick  on  which  the  granite  masonry  pier 
was  built.  The  piles  were  eaten  through  allowing  one  end  of 
the  pier  to  drop  2  feet.  When  several  pile  heads  were  cut  off, 
brought  to  the  surface  and  cut  open,  live  teredo  and  limnoria 
were  discovered,  although  the  location  was  within  200  feet  of 
the  mouth  of  a  sewer.  Whether  the  teredo,  due  to  its  objec- 
tion to  crossing  joints,  entering  beyond  a  certain  distance,  etc., 
would  destroy  the  deck  of  a  large  wooden  caisson,  is  an  open 
question,  but  the  danger  is  great  enough  to  rule  out  timber  in 
the  future  whenever  possible. 

There  are  some  accidents  or  errors  of  judgment  against  which 
the  designer  is  powerless.  For  instance,  one  of  the  best  super- 
intendents in  the  country  put  too  large  a  charge  of  dynamite 
outside  of  the  cutting  edge  to  break  up  the  rock  and  blew  out 
the  end  of  the  caisson.  Besides  making  it  a  total  wreck,  the 
jar  combined  with  an  extra  high  tide  broke  the  bond  between 
the  concrete  and  bedrock  in  an  adjoining  caisson,  about  200 
feet  away,  and  lifted  the  caisson  enough  to  require  its  removal 
and  rebuilding.  Numerous  cases  have  occurred  where  the  deck 
has  been  badly  warped  by  allowing  one  corner  to  land 
on  a  harder  substance  than  the  rest  of  the  cutting  edge,  or 
by  not  having  the  bed  dredged  to  a  uniform  depth  before 
placing  the  caisson.  One  of  the  Quebec  bridge  caissons  was 
thus  injured. 

ART.  183.     CAULKING,  SHAFTS  AND  LIGHTING 

One  of  the  advantages  of  concrete  caissons  is  the  absence 
of  joints  to  be  caulked.  In  steel  caissons  the  joints  must  be 
caulked  with  a  regular  caulking  tool,  while  in  wooden  caissons, 
every  joint  must  be  tightly  packed  with  oakum  and  often  with 
a^coat  of  pitch  also,  in  spite  of  which  there  is  a  considerable 
loss  of  air. 


ART.  183  CAULKING,   SHAFTS  AND  LIGHTING  545 

In  caulking  with  oakum,  one  man  can  cover  about  180  feet 
of  joint  in  a  day,  going  over  the  work  twice  but  using  only  a 
single  line  of  oakum.  In  wooden  or  steel  caissons,  it  is  very 
hard  to  get  a  water-  and  air-tight  job,  even  with  the  best  caulk- 
ing and  flushing  the  deck  with  mortar  before  placing  the  con- 
crete. No  one  likes  to  see  the  air  bubbling  up  through  the 
green  concrete,  much  less  to  see  it  form  a  water-spout  several 
feet  above  the  top  of  the  concrete.  In  New  York,  the  escape 
of  air  from  below  the  cutting  edge  or  elsewhere  has  been 
observed  in  buildings  from  100  to  200  feet  away. 

The  preceding  statements  about  caulking  the  side  walls  and 
deck  of  the  working  chamber  apply  even  in  a  higher  degree 
to  the  cofferdam  above  the  caisson,  especially  as  the  top  of 
the  concrete  may  be  many  feet  below  the  water  surface. 
A  small  leak  requires  pumping  and  this  is  the  greatest  enemy 
of  concrete. 

Small  caissons  under  4  or  5  feet  in  diameter  are  practically 
all  shaft,  but  in  larger  sizes,  one  or  more  inner  shafts  are  used 
to  take  men  and  material  in  and  out  of  the  caisson.  For  sizes 
up  to  12  or  15  feet  in  length,  it  is  customary  to  have  only  one 
shaft  for  both  men  and  material.  Sometimes  this  is  simply  a 
material  shaft,  3  feet  in  diameter,  with  a  ladder  set  in  the  side, 
while  at  other  times,  a  combined  shaft  is  used,  an  oblong  affair 
divided  into  two  compartments,  one  with  a  ladder  for  men  and 
the  otjier  for  taking  material  in  and  out. 

Whenever  the  size  of  the  caisson  permits,  there  should  be 
two  or  more  shafts  to  avoid  unnecessary  danger  to  the  men,  and 
also  to  facilitate  filling  the  air  chamber.  Temporary  failure 
of  the  lock  to  work,  or  the  jamming  of  a  bucket  in  the  shaft, 
has  often  held  the  men  as  prisoners  for  hours,  sometimes  more 
than  twelve,  and  sometimes  with  serious  loss  of  life.  On  the 
other  hand,  two  shafts  are  more  expensive  than  one,  even  al- 
lowing for  the  extra  handling  of  material,  and  contractors  do 
not  like  to  incur  the  extra  expenditure  of  time  and  money. 
But  several  shafts  do  not  always  insure  safety.  Some  years 
ago,  in  the  Passaic  River,  one  of  the  best  foremen  failed 
fasten  the  bucket  properly  to  the  hoisting  rope,  and 

35 


546  PNEUMATIC  CAISSON  PRACTICE  CHAP.  XVIII 

the  bucket  dropped  in  the  lock,  forced  the  bottom  door  open 
while  the  top  was  also  open,  thus  allowing  all  the  compressed 
air  to  escape  and  drowning  nearly  all  the  men  in  the  working 
chamber,  including  the  foreman  himself. 

If  the  shaft  is  made  of  steel  and  not  buried  in  concrete,  it 
should  be  f  inch  thick,  and  properly  fastened  so  that  neither 
shaft  nor  lock  can  be  blown  off,  as  has  sometimes  occurred. 
If  the  steel  shaft  is  buried  in  the  concrete,  it  may  be  built  of 
j-inch  metal,  provided  it  is  designed  so  that  it  cannot  be  blown 
off.  At  first,  it  was  customary  to  use  heavy  steel  shafts  which 
were  left  in  the  concrete,  but  this  proved  so  expensive  that  the 
plan  was  modified  to  leave  only  the  bottom  section  buried  in 
the  shaft,  its  length  not  exceeding  8  to  10  feet  and  sometimes 
only  18  inches.  The  rest  of  the  shaft  was  protected  from  the 
concrete  by  a  timber  box  surrounding  it.  But  as  the  concrete 
often  leaked  through  the  box  and  set  around  the  shaft,  prevent- 
ing its  removal,  and  causing  considerable  loss  to  the  con- 
tractor, two  other  methods  were  adopted  later.  In  the  first 
plan,  a  heavy  cast-iron  collapsible  shaft  is  used  which  is  removed 
after  the  air  chamber  is  filled.  In  the  second  plan,  timber 
forms  with  rungs  for  a  ladder  are  used  in  the  shaft  except  for 
the  upper  section  near  the  lock,  especial  care  being  taken  to 
provide  an  adequate  connection  of  the  steel  shaft  to  the  con- 
crete. A  number  of  fatal  accidents  have  occurred  in  which  the 
lock  was  blown  off  from  the  caisson. 

When  candles  were  employed  for  lighting,  there  was  con- 
stant danger  of  fire.  A  fire  started  in  the  joints  of  a  timber 
deck  and  fanned  by  compressed  air  is  very  difficult  to  put  out, 
even  by  flooding  the  working  chamber.  More  recently,  upon 
hoisting  a  bale  of  oakum  from  the  4-foot  joint  well  between 
two  caissons,  a  candle  in  the  lock  was  knocked  over,  the  rope 
set  on  fire  and  the  blazing  oakum  dropped  on  the  men 
below.  Two  men  were  burned  to  death  and  several  others 
seriously  injured. 

All  caissons  should  be  lighted  by  electricity  whenever  pos- 
sible, even  the  small  joint  caissons  between  the  main  ones,  as 
the  accident  just  cited  indicates.  Apart  from  the  danger  of 


ART.  184  METHODS   OF  LAUNCHING  547 

fire,  the  old  tallow  candle  was  never  satisfactory,  for  as  the  rate 
of  combustion  is  greater  in  compressed  air,  the  lungs  of  the 
workmen  are  so  filled  with  soot  that  many  days  are  required 
to  get  rid  of  it.  Electric-light  wires  are  generally  carried  down 
the  shaft  and  occasionally  a  bare  wire  will  charge  the  iron 
ladder  giving  an  unwelcome  shock  to  the  men  using  it. 

The  pipes,  3  or  4  inches  in  diameter,  which  convey  the 
compressed  air  to  the  working  chamber,  as  well  as  the  gas  pipe 
for  whistling  or  signalling  to  the  men  outside,  were  formerly 
left  in  the  concrete,  but  in  later  practice,  they  are  sometimes 
placed  in  a  pocket  next  to  the  shaft,  so  that  they  can  be  removed 
and  used  again.  The  same  arrangement  is  applied  to  the  pipes, 
about  5  inches  in  diameter,  which  are  used  to  blow  out  material 
when  that  method  is  suitable.  These  details  and  many  others 
cannot  be  designed  by  any  one  who  has  not  worked  in  a  caisson 
and  is  not  familiar  with  methods  of  operation,  without  making 
serious  blunders. 

ART.  184.     METHODS  OF  LAUNCHING 

There  are  practically  four  methods  of  getting  a  caisson  into 
the  water:  First,  when  built  on  shore,  it  is  skidded  into  the 
water  on  launching  ways;  second,  when  built  in  a  pontoon, 
the  pontoon  is  taken  away  underneath;  third,  when  built  on 
a  boat  or  wharf,  the  caisson  is  lifted  by  derricks  and  placed  in 
the  water;  and  fourth,  when  the  cutting  edge  is  supported  from 
a  temporary  platform  on  piles  or  boats,  and  is  then  lowered 
by  long  screw  rods,  or  block  and  tackle,  etc.,  to  a  firm 
bottom. 

When  built  on  shore  and  skidded  into  the  water,  no  more 
work  is  done  before  launching  than  is  necessary;  the  bottom  of 
all  shafts  should  be  closed  temporarily  and  a  small  amount  of 
grout  or  concrete  placed  on  the  deck  to  make  it  water-tight. 
A  caisson  of  ordinary  size  and  timber  construction  will  draw 
about  8  to  10  feet  of  water  when  floated  and  must  have  enough 
cofferdam  to  prevent  flooding.  A  failure  to  provide  skids  or 
runways  of  ample  strength  has  resulted  in  several  breakdowns 


548  PNEUMATIC   CAISSON   PRACTICE  CHAP.  XVIII 

before  launching,  with  a  loss  of  thousands  of  dollars  and  consider- 
able valuable  time. 

The  method  of  building  on  a  pontoon  is  very  satisfactory, 
especially  when  a  number  of  caissons  can  be  built  on  the  same 
pontoon.  A  pontoon  is  a  flat-bottomed  boat  with  vertical 
sides,  leaving  a  clear  space  of  about  5  feet  in  which  to'  work 
all  around  the  caisson.  The  bottom  is  constructed  of  12X12 
-inch  timbers  spaced  2  to  3  feet  apart,  to  which  4-inch 
planks  are  spiked  underneath.  The  sides  are  6  or  7  feet  high 
or  sufficient  to  prevent  any  danger  of  flooding  during  con- 
struction. Both  the  bottom  and  sides  are  thoroughly  caulked 
with  oakum. 

These  pontoons  are  made  of  two  or  more  parts  bolted  to- 
gether in  the  middle  and  so  arranged  that  after  the  caisson  has 
been  built  to  a  height  of  14  to  20  feet  above  the  cutting  edge, 
caulked,  with  shafts,  etc.,  in  place  and  properly  connected  to 
the  deck,  the  bolts  connecting  the  two  halves  can  be  removed. 
Stone  or  gravel  is  then  placed  on  the  center  of  the  pontoon,  and 
when  everything  is  ready  the  valves  are  opened,  allowing  the 
pontoon  to  fill  with  water  until  the  caisson  floats.  Sometimes 
the  arrangement  is  so  perfect  that  the  minute  the  caisson  floats 
the  two  halves  of  the  pontoon  shoot  from  under  and  the  launch- 
ing is  completed.  It  is  often  necessary,  however,  to  attach 
tugs  to  pull  the  sections  apart;  or,  by  means  of  struts  attached 
to  the  caisson  and  by  block  and  tackle,  the  pontoon  sections 
are  pushed  apart.  At  one  time  a  superintendent  forgot  to 
sink  the  pontoon  first  in  order  to  relieve  it  of  the  weight  of  the 
caisson,  and  upon  trying  to  pull  away  the  pontoon  sections,  he 
succeeded  merely  in  letting  in  water  enough  to  freeze  the 
caisson  to  the  pontoon;  accordingly,  it  took  two  weeks  instead 
of  about  three  minutes  to  launch  it.  At  Hartford,  where  seven 
caissons  were  23  feet  wide  and  two  were  46  feet  wide,  the  pon- 
toon was  built  for  the  smaller  size  and  additional  sections  were 
added  for  the  larger  size. 

Building  on  boats  or  shore  and  lifting  the  caissons  bodily  into 
the  water,  depends  upon  local  conditions,  and  applies  to  the 
smaller  caissons.  The  fourth  method  is  in  some  cases  the  only 


ART.  185  PLACING  AND  SINKING  549 

one  which  can  be  adopted  economically.  For  example,  at 
Pierre,  S.  D.,  the  bed  of  the  Missouri  River  consisted  of  very 
fine  silt  and  the  water  was  too  shallow  to  float  a  caisson;  if  a 
channel  10  feet  deep  were  dredged  out,  it  would  fill  up  before 
the  caisson  could  be  towed  into  place.  Piles  were  therefore 
driven  to  form  the  supports  for  a  platform  around  the  site  of 
each  caisson  and  about  32  rods  were  suspended  from  these 
platforms  in  such  a  way  that  the  cutting  edge  could  be  built 
upon  their  hooks  at  the  bottom.  After  the  caisson  was  built 
up  about  14  feet  above  the  cutting  edge,  it  was  lowered  by  si- 
multaneously turning  the  nuts  on  the  32  rods  until  the  cutting 
edge  came  to  rest  on  the  bottom.  The  rods  were  then  discon- 
nected for  use  on  the  next  caisson  while  building  up  the  coffer- 
dam and  concreting  were  continued.  It  took  from  10  to  12 
hours  to  lower  a  caisson. 

ART.  185.     PLACING  AND  SINKING 

Before  launching  a  caisson  and  lowering  it  to  position,  the 
site  must  be  prepared  by  excavating  the  higher  spots  to  a 
level  surface.  If  the  low  spots  are  filled,  they  are  not  as  firm 
as  the  other  material  and  thus  cause  trouble.  Leveling  the 
site  properly  is  especially  important  in  a  swift  current.  When 
possible,  guide  piles  are  driven  on  each  side  and  sometimes 
clusters  of  piles  are  driven  up-  and  downstream  to  which  lines 
are  attached  to  hold  the  caisson  in  position  until  it  is  sunk  deep 
enough  to  be  safe.  These  guide  frames  support  working  plat- 
forms, form  parts  of  supports  for  derricks  unless  they  are 
mounted  on  boats,  act  as  wharves  for  boats  of  stone,  sand  or 
cement,  and  for  the  sand  hogs'  boat.  In  some  cases,  it  is 
advantageous  to  build  a  temporary  island  of  gravel,  sand,  etc., 
on  which  to  build  the  caissons  in  position,  looking  out  for  the 
danger  of  floods,  since  some  rivers  rise  enough  in  24  hours 
to  wash  away  such  an  island. 

After  the  caisson  has  reached  the  proper  position,  the  shafts 
are  built  up  and  concreting  started  until  the  cutting  edge  has 
penetrated  far  enough  into  the  ground  to  make  it  safe  to  put 


550  PNEUMATIC   CAISSON   PRACTICE  CHAP.  XVIII 

on  air  and  send  down  the  sand  hogs.  In  the  Mohawk  river, 
caissons  were  started  on  artificial  islands,  while  in  the  Susque- 
hanna  river,  at  Havre  de  Grace,  they  had  to  be  sunk  through  60 
feet  of  water.  At  the  former  locality,  the  concrete  was  well 
above  the  water  surface  from  the  start  of  sinking,  while  at  the 
latter,  the  concrete  had  to  be  kept  25  to  30  feet  below  the 
surface  until  the  bottom  was  reached. 

The  ideal  condition  during  sinking  is  to  have  just  weight 
enough  to  keep  the  caisson  moving  gradually  and  continuously, 
with  the  cutting  edge  a  few  inches  below  the  excavation  in  the 
working  chamber,  until  the  final  position  is  reached,  but  it  is 
difficult  to  secure  this  condition.  If  a  caisson  is  too  heavy, 
it  is  liable  to  break  the  side  friction  and  fill  the  air  chamber 
with  sand,  and  if  it  is  not  heavy  enough,  as  frequently  happens, 
it  is  necessary  to  lower  the  air  pressure  to  start  the  movement, 
thus  giving  jerky  sinking. 

In  caissons  for  city  buildings,  it  is  a  common  occurrence 
to  see  the  excavation  carried  from  i  to  2  feet  below  the  cutting 
edge,  and  then  to  have  the  air  pressure  lowered  for  a  few  seconds, 
the  friction  being  suddenly  overcome,  and  the  caisson  sunk 
2  feet  or  more.  Sometimes,  however,  hundreds  of  tons  of 
pig-iron  or  cast-iron  blocks  are  piled  on  top  to  assist  the  opera- 
tion of  sinking.  The  caissons  for  the  Zinn  Building  in  New  York 
(see  Canadian  Engineer,  Feb.  22,  1912)  first  penetrated  made 
ground  and  the  Hudson  River  silt.  On  lowering  the  air  pressure 
the  friction  was  suddenly  overcome  and  the  caisson  sank  until 
sand  and  mud  filled  the  air  chamber,  resulting  in  the  loss  of 
a  shift  of  eight  hours.  This  accident  occurred  fifteen  times  at 
that  site,  sometimes  without  lowering  the  pressure;  a  record 
of  misfortune  which  has  never  been  equalled.  Fortunately 
the  men  were  in  the  shaft  when  it  happened  the  first  time  and 
were  On  the  watch  afterward. 

In  sinking  the  first  caisson  for  the  Municipal  Building  in 
New  York,  when  the  penetration  was  nearly  100  feet  below 
ground  water-level,  the  air  pipe  broke  and  within  15  minutes 
sand  filled  the  working  chamber  and  extended  16  feet  up  into 
the  shaft,  while  the  water  had  risen  42  feet  above  the  cutting 


ART.  185  PLACING  AND  SINKING  551 

edge.  The  men  were  on  the  way  up  the  shaft  when  the  connec- 
tion broke  and  the  water  followed  the  feet  of  the  last  man  nearly 
as  fast  as  he  could  climb.  If  plenty  of  weight  in  the  form  of  iron 
blocks  can  be  obtained  without  too  much  cost,  it  is  better  to 
use  it  in  sinking,  for  reducing  the  air  pressure  or  using  a  water- 
jet  is  almost  sure  to  increase  the  friction  for  the  next  drop,  with 
exasperating  results. 

It  is  essential  to  have  sufficient  outside  bracing  to  keep  the 
caisson  in  line  until  the  penetration  reaches  25  to  30  feet.  If 
it  gets  far  out  of  line  before  that,  it  is  almost  impossible  to 
plumb  it  again,  and  is  likely  to  get  out  of  line  still  more  as  it 
sinks.  If  it  is  nearly  plumb  at  that  depth,  there  is  rarely  much 
trouble  at  greater  depths.  The  more  it  is  out  of  plumb,  the 
more  is  the  caisson  apt  to  be  warped,  greatly  increasing  the 
frictional  resistance.  Very  few  caissons,  however,  are  less 
than  6  inches  out  of  plumb,  or  out  of  line,  and  a  greater 
allowance  than  this  should  always  be  made  in  designing 
foundations. 

It  is  useless  to  specify  that  no  caisson  will  be  accepted,  if  it 
is  more  than  6  inches  out  of  plumb  or  position,  if  sunk  to  any 
considerable  depth.  It  would  be  a  radical  remedy  to  remove 
a  caisson  sunk  from  40  to  90  feet  and  start  over  again,  for 
generally  the  loss  of  time  to  the  owner  would  be  sufficient  to 
prevent  enforcing  such  a  provision  against  the  contractor. 

Pneumatic  caissons  are  used  only  where  water  is  encountered, 
and  where  the  volume  of  water  is  too  great  to  permit  pump- 
ing in  an  open  cofferdam,  or  where  such  an  operation  would 
endanger  adjoining  structures  by  drawing  the  water  and  sand 
from  under  them  and  thus  allowing  settlement.  The  air 
pressure  must  be  just  sufficient  to  keep  the  water  from  flowing 
in  and  bringing  the  sand  with  it.  Even  when  much  care  is 
employed  with  compressed  air,  trouble  on  this  account  occurs 
frequently  and  sometimes  at  a  considerable  distance  away. 
For  instance,  while  sinking  the  foundations  for  Liberty  Tower 
in  New  York  City,  a  certain  quantity  of  water  and  sand  must 
have  escaped  from  under  the  Chamber  of  Commerce  Building 
on  the  opposite  side  of  the  street,  causing  the  interior  columns 


55 2  PNEUMATIC   CAISSON  PRACTICE  CHAP.  XVIII 

to  settle  considerably  while  the  outside  walls  were  apparently 
not  disturbed. 


ART.  186.    EXCAVATION  AND  SEALING 

Two  methods  are  in  use  for  removing  material  from  the  work- 
ing chamber:  First,  by  buckets  and  derricks;  and  second,  by 
blowing  it  out.  In  the  first  method,  the  sand  hogs  shovel  or 
lift  the  material  into  buckets  which  hold  about  a  third  of  a 
cubic  yard.  The  bucket  is  attached  to  a  cable  and  hoisted 
into  the  lock  at  the  top  of  the  shaft,  the  bottom  door  is  closed 
and  the  top  door  opened,  thus  allowing  the  bucket  to  be  swung 
clear  of  the  lock,  emptied  and  returned  to  the  caisson  for  another 
load  without  having  been  disconnected  from  the  cable.  Oc- 
casionally the  lock  has  no  top  door  but  one  at  the  side,  in  which 
case  the  bucket  is  dumped  while  still  in  the  lock.  Such  a  lock 
works  better  with  sandy  ground  than  with  sticky  clay.  The 
makers  claim  that  it  is  more  economical  than  other  locks, 
especially  for  small  sizes. 

When  conditions  permit  the  use  of  the  blow  method,  this 
is  the  cheapest.  It  requires  a  4-  or  5-inch  cast-iron  pipe  from 
the  surface  to  the  deck,  from  which  is  extended  a  flexible  hose 
with  a  valve  near  the  lower  end.  Above  the  surface  the  pipe 
must  have  a  bend  or  elbow  to  direct  the  material  away  from  the 
caisson.  In  operation,  the  material  is  shoveled  or  washed  into 
a  pile  at  the  end  of  the  hose,  and  the  valve  opened  to  let  the 
compressed  air  carry  it  out.  The  material  can  be  removed 
much  faster  than  it  can  be  shoveled  into  a  pile,  or  than  the  con- 
creting can  be  continued  at  the  top.  A  large  volume  of  air 
escapes,  while  gravel  and  even  fair-sized  stones  go  out  with 
such  terrific  velocity  that  a  cast-iron  elbow  2  inches  thick 
is  worn  through  in  an  hour.  In  one  instance,  the  windows  of 
a  tug  200  feet  away  were  broken.  Accordingly,  the  hardest 
manganese  steel  is  used  for  these  elbows.  While  waiting 
for  a  new  one  the  expedient  has  been  adopted  of  fastening  a 
'  i2-inch  block  of  wood  to  the  old  elbow. 

The  most  important  part  of  pneumatic  caisson  work  is  in 


ART.  1 86  EXCAVATION  AND  SEALING  553 

sealing  the  air  chamber,  or  filling  the  space  betwee'n  the  bottom 
of  the  excavation  and  the  deck  of  the  caisson  with  concrete. 
By  the  old  method,  the  concrete  was  spread  on  the  botton> 
until  it  extended  a  foot  or  two  above  the  cutting  edge,  and  then 
it  was  benched  up  around  the  sides,  using  boards  for  bulkheads 
if  necessary,  until  the  concrete  was  3  or  4  inches  below  the 
deck.  The  remaining  space  was  filled  by  ramming  into  it 
a  fairly  dry  mortar.  This  method  was  very  expensive  and 
unsatisfactory,  for  the  concrete  had  to  be  fairly  dry  to  stand 
benching.  Dry  concrete  should  never  be  used  in  compressed 
air,  since  the  moisture  is  absorbed  so  rapidly.  The  writer 
has  examined  old  work  and  found  the  concrete,  which  had 
been  placed  in  this  manner,  in  a  very  poor  condition.  He  has 
also  taken  out  concrete,  which  was  mixed  very  wet,  from  the 
bottom  of  a  caisson  and  found  it  to  be  exceptionally  good.  In 
another  method,  the  filling  was  continued  either  by  bucket  or 
concrete  chutes  until  the  wet  concrete  reached  the  roof.  Actual 
measurements  have  shown  a  space  of  \  to  f  inch  between  the 
concrete  and  the  deck  due  to  the  shrinking  of  the  concrete 
while  setting. 

The  writer's  present  practice  is  as  follows:  The  roof  is 
sloped  as  much  as  possible  and  air  vents  I  or  2  inches  in  diameter 
are  placed  as  far  as  possible  from  the  shaft  used  for  the  concrete. 
The  air  chamber  is  filled  with  very  wet  concrete  to  within  10  or 
12  inches  of  the  roof.  Meanwhile,  the  air  pressure  was  gradu- 
ally reduced  according  to  the  change  in  head  from  the  cutting 
edges  upward.  Work  is  then  suspended  for  at  least  24  hours 
under  air  pressure,  by  which  time  the  5  feet  of  concrete  will 
attain  its  permanent  shrinkage.  The  air-lock  is  then  taken  off 
and  concrete  is  dumped  down  the  shaft  to  fill  the  space  in  the 
air  chamber  and  some  distance  up  the  shaft.  This  concrete  is 
made  as  wet  as  possible,  while  grout  is  used  in  some  cases.  If 
properly  done,  it  will  be  found  that  the  air  has  all  been  forced 
up  the  vents  and  the  grout  from  the  concrete  stand  6  to 
20  feet  up  the  vent  pipes,  thus  indicating  that  the  chamber  is 
entirely  filled. 


554  PNEUMATIC   CAISSON  PRACTICE  CHAP.  XVIII 

ART.  187.    JOINTS  BETWEEN  CAISSONS 

There  are  several  methods  of  making  a  joint  between  two 
caissons  to  prevent  the  flow  of  water  between  them.  One 
method  is  by  stock  ramming,  as  applied  on  the  Mutual  Life 
Building  foundations  in  1900.  The  caissons  were  18  feet  wide, 
made  of  steel  and  filled  with  concrete.  They  were  kept  from 
getting  too  close  together  "by  two  6  X  6-inch  oak  strips,  spaced 
about  4  feet  apart  and  held  in  place  by  6  X 4-inch  steel  angles. 
Between  the  two  caissons  and  these  strips  a  4-inch  pipe  was 
forced  to  rock,  and  pellets  of  clay  were  rammed  down  the  pipe 
by  an  iron  rod  under  the  weight  of  a  pile-hammer.  This  method 
exerts  a  high  pressure  and  is  capable  of  doing  much  damage  if 
not  carefully  watched.  For  example,  in  trying  to  stop  a  leak  in 
a  dam,  500  cubic  yards  of  concrete  were  cracked  and  lifted  by 
the  force  of  the  clay  driven  through  one  pipe.  The  oak  strips 
referred  to  above  kept  the  clay  from  spreading  and  it  was  thus 
thoroughly  compacted  to  hold  back  the  water  while  the  cellar 
was  dug,  and  while  2  feet  of  brick  from  the  inside  face  was 
placed  between  the  ends  of  the  caissons  for  a  permanent  water- 
tight wall.  Forcing  down  grout  instead  of  clay  has  also  been 
tried,  but  did  not  prove  as  successful. 

On  the  Commercial  Cable  Building,  in  1896,  the  so-called 
half-moon  joint  was  used  for  the  first  time.  The  steel  caissons 
were  6  feet  wide  and  so  arranged  that  4  feet  of  the  end  walls  of 
each  caisson  could  be  removed  after  sinking.  Behind  these 
plates  timber  form!?  had  kept  the  concrete  back,  leaving  a  semi- 
circular opening,  so  that  the  two  adjoining  openings  formed  a 
shaft  about  4  feet  in  diameter  from  the  top  to  the  bottom. 
Before  removing  the  end  sections,  however,  stock  ramming  was 
applied  on  each  side,  with  the  result  that  the  clay  filled  not  only 
the  space  between  the  caissons,  but  spread  into  the  lot  as  far  as 
20  feet  in  extreme  cases.  After  the  sections  were  removed,  the 
vertical  shaft  was  cleaned  out  and  filled  with  concrete,  making 
for  the  first  time  a  continuous  concrete  wall  all  around  the  build- 
ing to  exclude  the  water. 

In  many  cases,  no  stock  ramming  was  used,  but  a  lock  at- 


ART.  1 88  PLANT  AND  EQUIPMENT  555 

tached  to  a  small  shaft  was  concreted  or  bolted  in  place  over 
the  3~or  4-foot  circular  shaft,  and  after  the  application  of  com- 
pressed air,  the  sand  hogs  closed  the  two  openings  in  the  shaft, 
working  downward  from  the  top  and  removing  the  material  at 
the  same  time.  This  is  often  done  by  nailing  short  boards 
against  upright  timbers  placed  in  the  ends  of  the  caissons 
before  sinking.  In  one  instance,  these  boards,  not  being  strong 
enough  or  properly  fastened,  were  blown  out  allowing  the  ground 
to  flow  in  and  kill  two  men  in  the  shaft  or  key-way.  To  close 
the  opening  between  the  caissons,  by  driving  sheet-piling 
on  each  side  before  applying  air,  is  quicker  and  cheaper  than 
stock  ramming  but  not  nearly  so  effective.  See  Art.  123  for 
illustrations. 

ART.  1 88.     PLANT  AND  EQUIPMENT 

The  pipes  to  supply  compressed  air  are  generally  4  inches 
in  diameter,  and  there  should  be  two  from  the  caisson  deck  to 
the  top  to  facilitate  changing  the  connection  as  the  cofferdam  is 
built  up.  One  4-inch  pipe  is  sufficient  from  the  caisson  to  the 
compressors,  with  smaller  pipes  for  high  pressure  to  operate  the 
locks.  In  winter  these  pipes  should  be  placed  in  a  box  filled 
with  manure  to  prevent  freezing. 

The  compressors,  electric-lighting  and  pumping  plants  are 
sometimes  compactly  arranged  on  a  big  float,  although  it  often 
pays  to  locate  them  on  shore  alongside  of  a  railroad  track  on 
account  of  coaling  facilities.  Where  an  old  bridge  is  located 
next  to  the  one  under  construction,  it  affords  a  good  support 
for  the  pipe  lines;  or  a  light  trestle  may  be  built  on  piles  to 
carry  them;  or  the  pipes  may  be  laid  on  the  river  bottom, 
although  this  is  not  so  desirable. 

It  is  impossible  to  lay  down  any  rigid  rule  for  the  size  of 
plant  required.  It  depends  both  on  the  number  of  caissons 
and  on  the  season  of  the  year  or  climatic  conditions.  It  always 
pays  to  have  plenty  of  boiler  capacity.  For  a  bridge  of  fair 
size  there  should  be  two  boilers  of  150  and  four  of  80  horse- 
power capacity  each.  There  should  always  be  one  more  air 


556  PNEUMATIC   CAISSON   PRACTICE  CHAP.  XVIII 

compressor  than  is  needed  for  constant  service,  to  allow  for 
repairs  that  will  certainly  be  required.  Nothing  is  so  expensive 
on  contract  work  as  delay.  A  work  of  this  magnitude  probably 
requires  three  or  four  compressors  with  an  aggregate  capacity 
of  2500  to  4000  cubic  feet  of  free  air  per  minute. 

In  illustration  of  the  effect  of  weather  and  location  on  the  cost 
of  work,  two  examples  are  given,  in  both  of  which  the  work 
extended  over  a  year  including  winter  and  summer.  The  first 
work  was  in  the  east  where  about  20  caissons  of  medium  size 
required  5000  tons  of  coal  at  a  cost  of  $15  ooo.  The  second  was 
in  the  west,  where  5000  tons  of  coal  were  also  required,  but  at 
a  cost  of  $40000.  Although  the  number  of  caissons  and  the 
total  yardage  of  caisson  work  were  only  about  one-half  as  large 
as  for  the  eastern  location,  yet  on  account  of  severe  weather 
and  higher  price,  the  coal  cost  over  five  times  as  much  per  cubic 
yard  of  caisson  work.  Both  jobs  were  handled  by  the  same 
contractor,  and  with  the  same  staff  and  plant.  This  fact  indi- 
cates why  it  is  so  difficult  to  compute  the  cost  of  pneumatic 
work  in  advance. 

One  of  the  best  money-saving  devices  for  a  contractor  who 
has  a  number  of  caissons  to  build  is  a  saw  arbor  run  by  com- 
pressed air  or  electricity.  The  time  saved  in  cutting  the  large 
timbers  to  the  right  length,  and  in  securing  small  timbers  of  the 
proper  dimensions,  pays  for  the  machine  in  a  short  time.  A 
good  pipe-cutting  machine  with  dies,  etc.,  is  also  indispensable, 
as  well  as  augers  to  bore  holes  for  bolts  and  drift  bolts  and  a 
hammer  to  drive  them,  both  run  by  compressed  air.  An  ample 
supply  of  the  best  stiff-leg  and  guy  derricks,  and  necessary  side 
tracks,  wharves,  cement  and  other  storage  buildings,  will  well 
repay  the  large  outlay  required.  Cable- ways  up  to  1600  fee  tin 
span  have  been  used  to  advantage  in  some  cases,  while  in  others 
they  proved  a  source  of  loss. 

ART.  189.     AIR-LOCKS  AND  CONCRETE 

One  of  the  most  important  contrivances  on  a  pneumatic 
caisson  job  is  an  air-lock,  without  which  the  work  cannot  be 
carried  on.  It  consists  of  an  air  chamber  with  one  door  opening 


ART.  189  AIR-LOCKS  AND  CONCRETE  557 

to  the  atmosphere  and  another  into  the  shaft  or  working 
chamber.  In  the  early  caissons,  the  lock  was  placed  below 
the  shaft  in  the  working  chamber.  This  is  an  inconvenient 
and  unsafe  position  for  the  lock,  for  if  the  caisson  becomes  too 
heavy,  there  is  danger  of  crushing  the  lock,  and  then  the  lock 
has  to  be  taken  apart  and  removed  before  the  shaft  can  be 
filled  with  concrete.  The  lock  was  probably  put  at  the  bottom 
to  permit  adding  new  sections  to  the  shaft  without  removing 
the  lock,  and  before  the  idea  occurred  to  any  one  of  placing 
an  additional  door  at  the  bottom  of  the  shaft.  This  door 
is  now  used  to  prevent  the  escape  of  air  when  the  lock  is 
lifted  off  temporarily  to  add  shafting.  It  is  also  useful  in 
case  of  emergency. 

Although  it  did  not  take  long  for  the  advantages  of  placing 
the  lock  at  the  top  of  the  shaft  to  become  apparent,  the  hoisting 
mechanism  was  placed  inside  of  the  lock.  Accordingly,  the 
bucket  was  lifted  from  the  working  chamber  into  the  lock,  the 
lower  door  closed,  and  the  material  dumped  through  a  side  door 
or  again  lifted  through  a  top  door,  thus  requiring  the  material 
to  be  handled  twice.  This  cumbersome  and  slow  method  is 
still  used  in  Europe  and  occasionally  in  this  country. 

This  arrangement  was  superseded  by  means  of  the  modern 
locks  which  permit  the  bucket  to  be  lowered  into  the  working 
chamber,  filled,  hoisted  out,  emptied,  and  returned  to  the  work- 
ing chamber  without  detaching  it  from  the  cable.  The  first 
lock  to  accomplish  this  saving  of  time  and  money  had  its  top 
door  in  two  horizontal  halves,  meeting  over  the  center  of  the 
shaft  and  leaving  a  hole  for  a  stuffing  box  3  or  4  inches  in  diame- 
ter at  the  center  of  the  joint.  The  stuffing  box  was  so  packed 
that  the  steel  cable  could  pass  through  freely  without  allowing 
much  air  to  escape.  When  the  bucket  was  hoisted  out  of  the 
lock,  the  stuffing  box  remained  on  the  cable  near  the  bale  of  the 
bucket.  Later  it  was  found  by  experiment  that  by  making 
the  hole  in  the  doors  only  large  enough  for  the  cable  to  pass 
through,  the  loss  of  air  was  not  sufficient  to  warrant  the  use  of  a 
patent  stuffing  box.  Since  there  is  no  necessity  for  the  cable 
to  pass  through  the  lower  door  of  the  lock  when  closed,  the  best 


558  PNEUMATIC   CAISSON  PRACTICE  CHAP.  XVIII 

form  is  a  single  round  door  slightly  larger  than  the  opening  and 
hinged  on  one  side.  It  is  known  as  a  flap  door  since  it  swings 
up  against  its  seat  where  it  is  held  by  air  pressure.  A  rubber 
gasket  about  |  inch  thick  and  3  to  4  inches  wide  is  usually  at- 
tached to  the  door  to  prevent  the  escape  of  air  between  the  door 
and  its  seat. 

According  to  present  practice,  then,  the  derrick  lowers  the 
bucket  into  the  lock,  the  upper  doors  close  against  the  cable, 
after  the  lock  is  filled  with  air  the  lower  door  drops  open  by  its 
own  weight  and  the  passage  is  clear  for  the  bucket  to  be  lowered 
into  the  working  chamber.  The  bucket  is  filled  and  hoisted 
again  into  the  lock,  the  lower  door  is  swung  up  by  levers  on  the 
outside,  the  air  in  the  lock  is  allowed  to  escape,  permitting  the 
upper  doors  to  be  opened  and  the  bucket  hoisted  out  and  emp- 
tied. The  entire  cycle  of  operation  for  a  half-yard  bucket  can 
be  repeated  20  times  an  hour,  a  vast  improvement  over  the 
older  system. 

Numerous  patents  have  been  taken  out  to  get  around  the 
original  one.  One  lock  has  a  circular  flap  door  at  the  top  as 
well  as  at  the  bottom,  the  upper  one  having  a  slot  extending 
from  the  center  to  the  edge  to  permit  the  door  to  shut  while  the 
bucket  is  suspended  in  the  lock.  An  additional  contrivance 
covers  the  slot  afterward.  Another  lock,  more  extensively 
used,  has  a  circular  top  door  so  placed  that  the  edge  of  the  door 
is  directly  over  the  center  of  the  shaft,  permitting  the  hole  for 
the  cable  to  be  located  at  the  edge  of  the  door  instead  of  the 
center.  This  arrangement  requires  the  lock  tender  to  give  the 
bucket  or  cable  a  slight  push  as  it  enters  or  leaves  the  lock.  In 
a  still  later  design,  the  cable  passes  through  the  door  frame 
instead  of  the  door.  Apparently  every  practicable  form  of  lock 
has  been  patented.  All  those  described  above  have  doors  open- 
ing inward,  so  that  when  they  are  closed  the  air  pressure  holds 
them  shut.  This  is  the  only  safe  method,  for  the  greater  the 
pressure,  the  tighter  the  door  is  held.  However,  locks  have 
been  built  with  upper  doors  closing  from  the  outside  and  held 
shut  by  means  of  screws,  etc.  When  the  bucket  is  taken  out 
of  the  lock,  the  door  and  stuffing  box  remain  on  the  cable. 


ART.  190  ALLOWABLE  BEARING  UNDER  CAISSONS  559 

But  few  of  the  locks  were  manufactured  as  the  patent  was 
promptly  bought  by  the  owner  of  other  patents. 

Bucket  locks  are  used  extensively  in  concreting  the  working 
chamber  as  well  as  in  excavating  small  caissons,  but  for  large 
caissons  having  two  shafts,  a  special  concrete  lock  is  used.  It 
usually  consists  of  an  ordinary  3-foot  shaft  with  a  door  in  the 
bottom,  and  a  cone  above  the  lower  door.  The  lock  is  placed 
on  top  of  the  shaft  and  has  a  hopper  located  above  it.  As  soon 
as  a  yard  or  so  of  concrete  has  been  dumped  into  the  lock,  the 
upper  door  is  closed  and  the  bottom  one  opened,  allowing  the 
mass  to  fall  down  the  shaft  into  the  working  chamber.  In 
this  manner,  concrete  can  be  taken  in  about  as  fast  as  the  men 
below  signal  for  it. 

All  concrete  for  caisson  work  should  be  as  non-porous  as 
possible.  The  principal  means  toward  this  end  consists  in 
making  the  mixture  of  sand  and  cement  in  the  proportion  of  one 
part,  by  volume,  of  cement  to  two  parts  of  clean,  sharp  and 
coarse  sand.  Four,  five,  or  even  more  parts  of  stone  or  gravel 
to  one  of  cement  can  be  used  for  this  mixture,  provided  it  is 
made  wet  enough.  A  poorer  mixture  than  one  to  two  of  cement 
and  sand  will  not  have  the  voids  of  the  sand  filled,  while  a  wet 
1-2-4  mixture  will  not  usually  have  as  much  stone  as  can  be 
safely  covered.  When  dry  concrete  used  to  be  employed,  it 
was  hard  to  get  a  1-2-4  mixture  properly  rammed,  but  with 
wet  concrete,  the  stone  immediately  disappears  in  the  cement 
and  sand,  insuring  good  concrete  without  voids. 

ART.  190.    ALLOWABLE  BEARING  UNDER  .CAISSONS 

The  maximum  pressure  allowed  on  bedrock  or  good  hard- 
pan  should  be  based  on  the  strength  of  concrete,  and  should 
never  exceed  15  tons  per  square  foot.  Good  concrete,  as  indi- 
cated by  careful  tests,  will  resist  very  much  higher  pressures, 
and  so  will  bedrock  and  many  kinds  of  hard-pan;  but  in  order 
to  allow  a  reasonable  factor  of  safety  to  cover  imperfect  work 
or  material,  even  if  such  lapses  occur  only  occasionally  in  the 
night,  this  pressure  should  not  be  exceeded. 


560  PNEUMATIC  CAISSON  PRACTICE  CHAP.  XVIII 

Good  sand  on  the  surface,  and  not  under  a  caisson,  should 
not  be  loaded  over  2  or  3  tons  per  square  foot;  but  if  it  is  under 
a  caisson  and  30  feet  or  more  below  the  surface  where  it  cannot 
be  disturbed,  it  can  safely  be  loaded  to  a  maximum  limit  of 
6  tons.  In  New  York  City,  the  hard-pan  varies  from  2  to  30 
feet  in  thickness,  with  30  to  60  feet  of  quicksand  above  it,  and 
sometimes  from  2  to  40  feet  of  sand,  boulders,  etc.,  below  it. 
It  also  varies  in  quality  from  a  material  resembling  good  con- 
crete to  that  of  loose  sand.  For  clay  and  other  materials,  the 
variations  are  so  great  that  no  definite  load  should  be  specified 
until  the  local  conditions  of  each  case  have  been  carefully  ex- 
amined and  considered. 

In  one  example,  open  concrete  cylinders  were  sunk  from 
30  to  90  feet  to  beds  of  various  grades  of  fine  and  coarse  sand. 
The  one  which  was  apparently  the  most  unfavorable  was  sub- 
jected to  a  test  load  of  10  tons  per  square  foot,  causing  a  settle- 
ment of  about  I  inch,  one-half  of  which  was  recovered  upon 
removing  the  load.  After  a  concrete  viaduct  to  carry  a  railroad 
was  built  upon  these  cylinders,  several  of  them  began  to  settle, 
and  continued  until  at  the  end  of  about  a  year  the  maximum 
was  reached,  some  cases  amounting  to  6  inches.  After  that  no 
further  trouble  occurred. 

ART.  191.     REMARKS  ON  UNDERPINNING 

Since  Chap.  XVI  on  underpinning  is  so  complete,  but 
little  remains  to  be  added  except  to  present  conclusions.  It  is 
generally  found  to  be  more  economical  to  use  inclined  shores, 
needles,  or  both,  on  light  buildings;  that  is,  on  ordinary  buildings 
up  to  six  or  seven  stories  high.  For  higher  buildings,  or  where 
bedrock  is  easily  accessible,  the  system  patented  by  BREUCHAUD 
in  1896  can  be  depended  upon  to  give  good  results,  but  it  is  not 
recommended  to  use  smaller  diameters  than  30  inches,  which 
permit  sending  men  down  to  the  bottom.  The  more  recent 
patented  systems,  namely,  MERRILL'S  telescopic  method 
and  THOMSON'S  vertical  tunnel  method,  are  fully  described  in 
Chap.  XVI. 


ART.  191  REMARKS   ON  UNDERPINNING  561 

In  the  writer's  experience,  1 6-inch  cylinders  have  been 
jacked  down  under  a  six-story  building  until  the  weight  of  the 
old  building  was  taken  off  the  old  foundations,  and  then  after 
the  shoring  was  completed,  these  cylinders  settled  when  an 
adjoining  caisson  was  sunk,  thus  requiring  the  use  of  inclined 
shores  after  all.  Later,  when  the  Gillender  Building  was 
removed  to  give  place  to  the  Bankers'  Trust  Building,  he  wit^ 
nessed  the  removal  (in  1911)  of  14-inch  cylinders  which  had 
been  sunk  in  1877  under  an  adjoining  building,  and  they  were 
found  to  be  filled  with  excellent  concrete  except  within  a  few 
feet  at  the  bottom,  which  was  filled  with  sand.  This  observa- 
tion probably  accounts  for  the  settlement  just  mentioned. 


CHAPTER  XIX 

REFERENCES  TO  ENGINEERING  LITERATURE 
ART.  192.    LITERATURE  ON  FOUNDATIONS 

Very  few  books  have  been  published  in  this  country  which 
are  devoted  exclusively  to  the  subject  of  foundations.  In 
most  cases  the  subject  is  treated  in  one  or  two  chapters  of  a 
book,  as  indicated  in  the  following  list.  The  list  is  not  complete 
but  contains  the  most  important  works  which  should  be  ac- 
cessible in  college  libraries.  With  a  few  exceptions,  only 
American  works  are  included.  The  dates  of  publication  given 
are  those  of  the  first  editions  of  the  respective  works. 

American  School  of  Correspondence.  Cyclopedia  of  Architecture, 
Carpentry  and  Building.  Chicago,  1907.  Vol.  3  contains  22  pages  on 
foundations. 

ARTHUR,  WILLIAM. — Contractors'  and  Builders'  Handbook.  New 
York,  1911.  Contains  one  chapter  (18  pages)  on  foundations, 
j/  BAKER,  I.  O. — Treatise  on  Masonry  Construction.  New  York,  1889. 
The  tenth  edition  contains  four  chapters  on  foundations,  the  titles  of 
which  are:  Introductory;  ordinary  foundations;  pile  foundations;  and 
foundations  under  water;  covering  about  18  percent  of  the  volume. 
Bridge  abutments  and  piers  are  treated  in  two  additional  chapters. 

BUEL,  A.  W.,  and  HILL,  C.  S. — Reinforced  Concrete.  New  York, 
1904.  The  second  edition  contains  28  pages  on  reinforced- concrete 
footings  and  on  concrete  piles. 

BYRNE,  A.  T. — Inspector's  Pocket-Book.  Materials  and  Workman- 
ship in  Construction.  New  York,  1892.  The  third  edition  contains  29 
pages  on  foundations. 

^CORTHELL,  E.  L. — Allowable  Pressures  on  Deep  Foundations.  New 
York,  1907.  The  entire  book,  containing  98  pages  and  8  folding  tables, 
is  devoted  to  a  record  of  pressures  on  deep  foundations  for  178  structures 
of  different  kinds  located  in  different  countries,  as  well  as  of  the  condi- 
tions in  the  respective  cases. 

FIEBEGER,  G.  J. — Civil  Engineering.  New  York,  1905.  One 
chapter  is  devoted  to  foundations. 

FOSTER,  W.  C.— Treatise  on  Wooden  Trestle  Bridges.     New  York, 

562 


ART.  192  LITERATURE    ON    FOUNDATIONS  563 

1891.  The  fourth  edition  contains  three  chapters  on  pile-bents,  pile- 
drivers,  and  concrete  [pile]  trestles.  That  on  pile-bents  includes  some 
notes  on  pile  driving. 

**  FOWLER,  C.  E. — Subaqueous  Foundations.  New  York,  1914.  This 
work  supersedes  Fowler's  Cofferdam  Process  for  Piers,  first  published  in 
1898,  and  his  Ordinary  Foundations,  under  which  title  the  second  edition 
was  published  in  1905. 

FREITAG,  J.  K. — Architectural  Engineering.  New  York,  1895.  Con- 
tains one  chapter  on  the  foundations  of  buildings,  relating  principally  to 
steel-grillage  and  reinforced-concrete  footings,  with  some  data  on  founda- 
tion loads. 

FRYE,  A.  L. — Civil  Engineers'  Pocket-Book.  New  York,  1913.  Con- 
tains one  section,  29  pages,  on  foundations. 

GILBERT,  G.  H.,  WIGHTMAN,  L.  J.,  and  SAUNDERS,  W.  L. — Subways 
and  Tunnels  of  New  York.  Methods  and  Costs.  New  York,  1912. 
In  one  appendix  12  pages  are  devoted  to  the  sinking  of  pneumatic  caissons 
for  tall  buildings  in  New  York.  Several  other  appendices  give  informa- 
tion on  the  use  of  compressed  air  for  tunnel  work,  shaft  sinking,  etc.,  and 
on  the  equipment  required. 

GILLETTE,  H.  P.,  and  HILL,  C.  S. — Concrete  Construction,  Methods 
and  Cost.  New  York  and  Chicago,  1908.  Contains  one  chapter  on 
methods  and  cost  of  concrete  and  pier  construction. 

GILLETTE,  H.  P. — Handbook  of  Cost  Data  for  Contractors  and  Engi- 
neers. New  York,  1906.  Includes  data  on  the  cost  of  piles,  drivers,  mak- 
ing piles,  driving  piles,  sawing-off  piles,  pulling  piles,  blasting  piles, 
puddle,  a  bridge  foundation  and  cofferdam. 

HARCOURT,  L.  F.  VERNON. — Civil  Engineering  as  Applied  to  Construc- 
tion. London,  1902.  Contains  one  chapter  on  foundations  and  piers  of 
bridges,  and  another  one  on  excavations,  dredging,  pile  driving,  and 
cofferdams. 

HILL,  LEONARD. — Caisson  Sickness  and  the  Physiology  of  Work  in 
Compressed  Air.  London,  1912. 

HOOL,  G.  A. — Reinforced-Concrete  Construction.  Vol.  2.  Retaining 
Walls  and  Buildings.  New  York,  1913.  One  chapter  (49  pages)  is 
devoted  to  foundations,  including  the  bearing  capacity  of  soils,  shallow 
footings,  and  concrete  piles.  Another  chapter  on  retaining  walls  includes 
designs  of  their  footings. 

International  Library  of  Technology.  Scranton,  1905.  Volume  52 
contains  section  18  (189  pages)  on  the  simple  types  of  footings  and  but- 
tresses, and  section  20  (70  pages)  on  shallow  foundations  and  cantilever 
foundation  girders. 

KIDDER,  F.  E. — Architect's  and  Builder's  Pocket-Book.  New  York, 
1884.  The  fifteenth  edition  contains  one  chapter  (about  65  pages)  on 
foundations  and  spread  footings. 


564         REFERENCES    TO    ENGINEERING   LITERATURE       CHAP.  XIX 

KIDDER,  F.  E. — Building  Construction  and  Superintendence.  Part  I. 
Masons'  Work.  New  York,  1896.  Contains  three  chapters,  respec- 
tively, on  foundations  on  firm  soils;  on  foundations  on  compressible  soils; 
and  on  masonry  footings  and  foundation  walls,  shoring  and  underpinning. 

MAHAN,  D.  H. — Treatise  on  Civil  Engineering.  New  York,  1873. 
Contains  two  chapters  on  foundations  of  structures  on  land,  and  in  water, 
respectively.  This  work  is  out  of  print. 

MERRIMAN,  M.,  Editor  in  Chief. — American  Civil  Engineer's  Pocket- 
Book.  New  York,  1911.  Contains  35  pages  on  foundations  on  land 
and  under  water;  and  some  other  articles  on  foundations  of  reinforced 
concrete,  on  shafts  and  borings,  etc. 

MITCHELL,  C.  F. — Building  Construction.  London,  1913.  (Seventh 
edition.)  Contains  one  chapter  on  foundations,  including  piles,  wall  and 
column  footings,  drainage,  and  shaft  sinking  and  trenching. 
^  PATTON,  W.  M. — Practical  Treatise  on  Foundations.  New  York,  1893. 
In  the  second  edition  about  50  percent  of  the  book  is  devoted  to  the 
subject  of  foundations  proper.  In  the  first  edition,  the  corresponding 
percentage  was  only  27. 

PATTON,  W.  M. — Treatise  on  Civil  Engineering.  New  York,  1895. 
Contains  one  chapter  on  foundations  and  foundation  beds. 

POWELL,  G.  T. — Foundations  and  Foundation  Walls.  New  York, 
1884.  An  elementary  treatise  on  the  foundations  of  ordinary  buildings. 

REID,  H.  A. — Concrete  and  Reinforced-Concrete  Construction.  New 
York,  1907.  Contains  one  chapter  on  foundations,  devoted  practically 
to  shallow  footings  and  reinforced-concrete  piles. 

RICKEY,  H.  G. — Building  Foreman's  Pocket-Book  and  Ready  Reference. 
New  York,  1909.  Contains  8  pages  on  piles  for  foundations. 

RICKEY,  H.  G. — Handbook  for  Superintendents  of  Construction, 
Architects,  Builders  and  Building  Inspectors.  New  York,  1905.  Con- 
tains 25  pages  on  pile  foundations  and  shallow  footings. 

TAYLOR,  F.  W.,  and  THOMPSON,  S.  E. — Treatise  on  Concrete,  Plain 
and  Reinforced.  New  York,  1905.  The  second  edition  contains  one 
chapter  (20  pages)  on  foundations  and  piers,  treating  particularly  of  single 
and  combined  footings  of  reinforced  concrete  and  of  concrete  piles. 

TAYLOR,  F.  N. — Manual  of  Civil  Engineering  Practice.  London,  1911. 
Contains  one  chapter  on  foundations  and  pile  driving. 

TRAUTWINE,  J.  C.,  J.  C.  JR.,  and  J.  C.  3rd.— Civil  Engineers'  Pocket- 
Book.  New  York,  1872.  The  nineteenth  edition  contains  one  section 
of  1 8  pages  on  foundations. 

WHEELER,  J.  B. — Elementary  Course  of  Civil  Engineering.  New 
York,  1876.  Contains  two  chapters  on  foundations  on  land  and  in  water, 
respectively.  Out  of  print. 

"     WHITE,  LAZARUS. — The  Catskill  Water  Supply  of  New  York  City. 
New  York,  1913.       One  chapter  gives  descriptions  of  borings  and  sub- 


ART.  192  LITERATURE    ON   FOUNDATIONS  565 

surface  investigations,  and  another  one  of  exploration  for  the  Hudson 
River  crossing,  including  49  pages  in  all. 

The  following  valuable  monographs  on  important  bridges 
and  their  foundations  have  been  published  in  book  form. 
They  deserve  study  by  engineers  with  reference  to  the  historical 
development  of  American  foundation  practice. 

CLARKE,  T.  C— The  Quincy  Bridge.  New  York,  1869.  Three  chap- 
ters and  an  appendix  are  devoted  to  the  physical  characteristics  of  the 
Mississippi  River,  a  description  of  the  substructure  and  foundations, 
specifications  and  classified  cost.  The  foundations  and  equipment  for 
construction  are  illustrated  by  12  plates.  The  open  caissons,  and  coffer- 
dams with  removable  sides  on  grillage,  were  used  for  pile  foundations, 
protected  from  scour  by  loaded  timber  cribs. 

CHANUTE,  OCTAVE,  and  MORISON,  GEORGE. — The  Kansas  City  Bridge. 
New  York,  1870.  Four  chapters  give  the  regimen  of  the  Missouri  River, 
the  foundations,  masonry,  and  classified  cost  of  the  work;  an  appendix 
gives  tables  showing  the  progress  of  sinking  a  pier,  with  soundings, 
weights,  etc.;  while  6  plates  illustrate  foundation  works,  piers,  and  equip- 
ment. Four  piers  were  founded  on  bed-rock  with  open  timber  caissons 
having  dredging  wells,  while  two  piers  were  founded  on  piles. 

WOODWARD,  C.  M. — History  of  the  St.  Louis  Bridge.  St.  Louis,  1881. 
Six  chapters  are  devoted  to  the  deep  pneumatic  foundations  for  the  two 
river  piers  and  east  abutment,  the  physiological  effects  of  compressed  air, 
computations  on  the  stability  of  the  piers,  and  on  classified  costs.  Two 
other  chapters  relate  to  the  west  abutment  which  required  a  cofferdam 
to  be  built  under  extraordinary  difficulties,  to  financial  and  engineering 
considerations  relating  to  preliminary  and  final  foundation  plans,  and  to 
sinking  by  the  pneumatic  process.  The  substructure  and  foundations  are 
illustrated  by  15  plates  of  plans  and  views. 

MORISON,  GEORGE  S.— Plattsmouth  Bridge,  1882;  Bismarck  Bridge, 
1884;  Blair  Crossing  Bridge,  1886;  New  Omaha  Bridge,  1889;  Rulo  Bridge, 
1890;  Sioux  City  Bridge,  1891;  Nebraska  City  Bridge,  1892;  Cairo  Bridge, 
1892;  Bellefontaine  Bridge,  1894;  Memphis  Bridge,  1894.  These  reports 
give  the  most  complete  information  about  pneumatic  foundations  of  any 
that  have  been  published.  The  kinds  of  data  given  are  indicated  by  the 
report  on  the  Bellefontaine  Bridge.  The  general  description  includes  the 
trestle  approach  on  piles,  the  classified  cost  of  each  pneumatic  foundation 
in  detail,  and  the  cost  and  quantity  of  masonry  in  the  piers.  In  ap- 
pendices are  given  a  record  of  sinking  the  caissons  with  elevations,  im- 
mersion, weights,  air  pressure,  and  skin  friction;  the  time,  costs,  and 
materials  used  in  foundations;  and  the  specifications  for  masonry.  The 


566         REFERENCES   TO    ENGINEERING   LITERATURE      CHAP.  XIX 

plates  show  elevations  and  plans  of  the  piers;  detail  drawings  of  the 
caissons;  a  diagram  giving  the  rate  of  progress  in  sinking  caissons;  and  a 
water-gage  record.  In  most  cases  a  record  of  the  preliminary  borings  is 
also  given.  In  the  first  two  reports,  however,  the  weights  and  skin  friction 
for  the  caissons,  computed  daily  while  sinking,  are  not  given. 

HUTTON,  W.  R.— The  Washington  Bridge.  New  York,  1889.  In  20 
pages  the  text  gives  a  brief  description  of  the  substructure,  the  specifica- 
tions for  the  masonry,  a  table  of  diamond  drill  borings,  and  a  record  of 
sinking  the  pneumatic  caisson.  The  illustrations  include  4  plates  on 
foundations  besides  20  on  masonry. 

BOLLER,  A.  P.— The  Thames  River  Bridge.  New  York,  1890.  The 
text  gives  a  record  of  soundings  and  borings,  a  description  of  foundations, 
weights  and  settlement  of  piers.  Three  plates  have  illustrations  on 
foundations.  Four  of  the  piers  are  supported  by  pile  foundations,  the 
upper  parts  of  the  piles  being  protected  by  timber  cribs  sunk  into  holes 
previously  dredged.  The  masonry  was  built  in  cofferdams  with  re- 
movable sides  on  grillage,  and  sunk  to  bearing  on  the  piles.  After 
removing  the  cofferdams,  a  filling  of  sand  and  gravel  was  placed  around 
the  piers  and  in  the  cribs. 

NOBLE,  ALFRED,  and  MODJESKI,  RALPH. — The  Thebes  Bridge.  Chi- 
cago, 1907.  The  description  of  the  substructure  is  supplemented  by  14 
plates  and  several  half-tone  views.  The  river  piers  were  founded  by  the 
pneumatic  process,  and  one  of  the  shore  piers  by  means  of  an  open  caisson 
of  reinforced  concrete.  The  specifications  for  the  substructure  are  given 
in  an  appendix. 

Cambridge  Bridge  Commission.  Report  of  the  Commission  and  ot  the 
Chief  Engieeer  (WILLIAM  JACKSON)  upon  the  Construction  of  the  Cam- 
bridge Bridge.  Boston,  1909.  The  description  of  the  substructure  and 
the  analysis  of  its  cost  are  supplemented  by  12  views,  n  folding  plates  and 
6  folding  schedules  of  expenditures.  The  piers  and  abutments  are  all 
supported  on  pile  foundations. 

MODJESKI,  RALPH. — The  Vancouver- Portland  Bridges.  Chicago, 
1910.  The  description  of  the  substructure  is  illustrated  by  23  plates. 
The  specifications  are  given  in  an  appendix.  This  report  includes  the 
Washington  Channel  bridge  over  the  Columbia  River,  Shaw's  (or  Hay- 
den's)  Island  viaduct,  the  Oregon  Slough  bridge,  and  the  Willamette 
River  bridge.  The  piers  of  the  bridges  over  the  two  rivers  were  founded  by 
the  pneumatic  process  while  the  abutments  and  the  remaining  piers  have 
pile  foundations. 

A  large  number  of  selected  references  to  engineering  periodi- 
cals and  the  proceedings  or  transactions  of  engineering  societies 
are  given  in  the  following  articles.  They  are  intended  for  the 


ART.  193  TIMBER   PILES    AND   PILE   DRIVING  567 

benefit  of  those  who  desire  to  study  any  topic  more  extensively 
or  in  greater  detail  than  the  limits  of  this  volume  allow  for  the 
descriptions  and  illustrations  given  in  the  text.  No  attempt  is 
made  to  refer  to  all  the  engineering  periodicals  published  in 
this  country,  nor  to  include  every  reference  that  may  be  found 
in  the  periodicals  selected.  It  will  be  observed  that  the  titles 
of  the  following  articles  in  this  chapter  correspond  to  those  of 
preceding  chapters.  The  authors  will  appreciate  information 
regarding  errors  discovered  in  the  references. 

It  is  a  valuable  exercise  for  the  student  to  compare  the  general 
arrangement  and  details  of  construction  for  any  given  type  of 
structure  relating  to  foundations,  as  designed  by  different 
engineers,  and  to  note  which  features  constitute  the  essential 
elements  of  that  type,  and  which  ones  are  dependent  merely 
upon  local  conditions  and  therefore  subject  to  more  or  less 
variation.  To  make  the  results  of  such  studies  readily  available 
for  future  reference,  they  should  be  placed  upon  separate  sheets 
of  paper  and  filed  in  accordance  with  a  suitable  classification  of 
subjects. 

ART  193.     TIMBER  PILES  AND  PILE  DRIVING 

TIMBER  PILES. — Tough  Pine  Piles  from  Nova  Scotia.  Eng.  News,  v. 
22,  p.  368,  Oct.  19,  1889.  Life  of  Different  Kinds  of  Timber  Piles. 
Report  of  Committee  and  Discussion.  Proc.  Assoc.  Ry.  Supts.  B.  &  B., 
1899,  v.  9,  p.  50.  Calculating  the  Cubical  Contents  of  Piling.  Eng. 
News,  v.  54,  p.  170,  Aug.  17,1905.  Table  prepared  by  E.  O.  Faulkner 
of  A.  T.  &  S.  F.  Ry.  See  Richey's  Building  Foreman's  Pocket-Book, 

PP-  474,  475- 

ORDINARY  PILE-DRIVERS. — Pile-Hammer  Ropes.  Including  tests. 
Proc.  Assoc.  Ry.  Supts.  B.  &  B.,  1897,  v.  7,  p.  250.  Repairing  a  leaking 
cofferdam;  and  pile  driving  methods  at  Leech  Lake,  Eng.  News,  v.  46,  p. 
189,  Sept.  19,  1901.  Driving  Difficult  Piles  for  Bridge  Renewal.  Eng. 
Rec.,  v.  43,  p.  54,  January  19,  1901.  Electric  Pile-Driver  and  Derrick. 
Eng.  News,  v.  47,  p.  513,  June  26,  1902  Sectional  Elevation  of  Apparatus 
for  Subaqueous  Pile  Driving.  Chas.  Sooysmith.  Eng.  News,  v.  48,  p.  472, 
December  4,  1902.  An  Excellent  Type  of  Land  Pile-Driver.  Eng. 
News,  v.  50,  p.  66,  July  16,  1903.  A  Novel  Tilting  Pile-Driver. 
J.  H.  Baer.  Eng.  News,  v.  50,  p.  205,  Sept.  3,  1903.  A  Chute  for 
Driving  Batter  Piles.  Eng.  Rec.,  v.  50,  p.  56,  July  9,  1904.  Derricks 


568         REFERENCES    TO   ENGINEERING   LITERATURE      CHAP.  XIX 

and  Sheet-Pile  Drivers  for  Foundation  Work.  Eng.  Rec.,  v.  50,  p.  254, 
Aug.  27,  1904.  Steel  Sheet-Piling  for  a  Boiler  Room  Excavation. 
Eng.  Rec.,  v.  52,  p.  472,  Oct.  21,  1905.  Steam  Pile  and  Sheet-Pile 
Drivers  on  the  New  York  Barge  Canal.  Emile  Low.  Eng.  Rec.,  v.  55,  p. 
298,  Mar.  2,  1907.  A  Pile  Trestle  Erected  with  a  Pivotal  Pile-Driver.  R. 
Balfour.  Eng.  News,  v.  58,  p.  160,  Aug.  15,  1907.  Highest  Pile-Driver. 
I.  H.  Frederickson.  Eng.  News,  v.  58,  p.  173,  £ug.  15,  1907.  Non- 
Patented  Pivotal  Pile-Driver.  Charles  Hansel.  Eng.  News,  v.  58. 
p.  201,  Aug.  22,  1907.  Telescoping  Leads  for  Pile-Drivers.  H.  P, 
Shoemaker.  Eng.  News,  v.  48,  p.  524,  Nov.  14,  1907.  Revolving  Pile- 
Driver.  Eng.  News,  v.  59,  p.  368,  April  2,  1908.  Driving  Long  Piles 
with  Short  Leads.  Frank  B.  McLean.  Eng.  News,  v.  60,  p.  41,  July  9, 
1908.  Steel  Pile-Driver  Leads.  Eng.  Rec.,  v.  63, p.  250,  Mar.  4,  1911. 
Roller  Case  Pile-Driver  used  in  the  construction  of  permanent  Trestle 
Extension  on  the  Ogden-Lucin  Cut-off.  C.  M.  Kurtz.  Eng.  News,  v.  66, 
p.  338,  Sept.  21,  1911. 

TRACK  PILE-DRIVERS. — Best  and  most  Economical  Railway  Track 
Pile-Driver.  Proc.  Assoc.  Ry.  Supts.  B.  &  B.,  1896,  v.  6,  p.  197.  Rail- 
way Pile-Driver.  G.  W.  Smith.  Jour.  W.  Soc.  Engrs.,  v.  4,  p.  251,  June, 
1899;  Eng.  News,  v.  42,  p.  314,  Nov.  16,  1899;  Eng.  Rec.,  v.  41,  p.  154, 
Feb.  17,  1900.  Best  Design  and  Recent  Practice  in  Building  Railroad 
Track  Pile-Drivers.  Proc.  Assoc.  Ry.  Supt.  B.  &  B.,  v.  12,  p.  163, 
Oct.,  1902;  Eng.  News,  v.  48,  p.  363,  Oct.  30,  1902.  Improved  and 
Combination  Collapsible  Pile-Drivers  for  Railroad  work.  Eng.  Rec.,  v.  49, 
p.  358,  Mar.  19,  1904.  Interstate  Ry.  Pile-Drivers.  Ry.  Age  Gaz.,  v. 
46,  p.  677,  Mar.  19,  1909.  High  Powered  Locomotive  Pile-Driver 
Carrying  its  own  Turntable.  Walter  Ferris.  Eng.  News,  v.  62,  538, 
Nov.  18,  1909;  Ry.  Age  Gaz.,v.  47,  p.  998,  Nov.  19,  1909.  Reprinted 
from  Jour.  Am.  Soc.  M.  E.,  Jan.,  1909.  Pile-Driver  Leads  on  a  Loco- 
motive Crane.  Eng.  Rec.,  v.  64,  p.  608,  Nov.  18,  1911.  Driving 
Trestle  Piles  with  a  Locomotive  Crane.  Eng.  News,  v.  66,  p.  625,  Nov.  23, 
191 1.  Desirable  Features  of  a  Track  Pile-Driver.  Proc.  Am.  Ry.  Eng. 
Assoc.,  1911,  v.  12,  p.  286,  Parti.  Convertible  Railway  Pile-Driver  and 
Locomotive  Crane.  Eng.  News,  v.  71,  p.  374,  Feb.  12,  1914. 

EQUIPMENT. — Crane's  Steam  Pile-Hammer.  Eng.  Rec.,  v.  15,  p.  372, 
Mar.  12,  1887.  Why  the  Nasmyth  Steam- Hammer  has  not  displaced 
the  Friction- Clutch  Pile-Driver.  Eng.  News,  v.  50,  p.  13,  July  2,  1903. 
Direct-Acting  Steam  Pile-Hammer.  Eng.  News,  v.  36,  p.  38,  July  16, 
1896.  New  Design  of  Steam  Pile-Driver.  Comparison  of  Several 
Types  of  Drivers.  A.  A.  Goubert.  Eng.  News,  v.  63,  p.  79,  Jan.  20, 
1910.  Goubert  Pile-Driving  Hammer.  R.  R.  Age  Gaz.,  v.  48,  p.  216, 
Jan.  28,  1910.  Advantages  and  Disadvantages  of  a  Steam  Pile-Driving 
Hammer.  Eugene  Lentilhon.  Eng.  News,  v.  36,  p.  58,  June  23,  1906. 
Observations  on  Driving  Piles  with  a  Steam-Hammer.  J.  J.  Welsh. 


ARI.  193  TIMBER   PILES   AND   PILE   DRIVING  569 

Jour.  Assoc.  Eng.  Soc.,  v.  33,  p.  193,  Sept.,  1904.  S team-Hammers  vs. 
Drop  Hammers  for  Pile-Drivers.  Report  of  Committee.  Proc.  Assoc. 
Ry.  Supts.  B.  &  B.,  v.  14,  p.  200,  Oct.,  1904;  R.  R.  Gaz.  v.  37, p. 501,  Oct. 
28,1904;  Eng.  News,  v.  52,  p.  378,  Oct.  27,  1904.  Pile-Driving  Notes. 
J.  E.  Crawford.  Eng.  News,  v.  61,  p.  622,  June  10,  1909.  Pile  Rings 
and  Method  of  Protecting  Pile  Heads  in  Driving.  Report  of  Committee 
and  Discussion.  Proc.  Assoc.  Ry.  Supts.  B.  &  B.,  1898,  v.  8,  p.  60. 
Protecting  Pile  Heads.  Report  of  Committee.  Proc.  Assoc.  Ry.  Supt. 

B.  &  B.,  v.  8,  p.  60,  Oct.,  1898;  Eng.  Rec.,  v.  38,  p.  450,  Oct.  22,  1898. 
Is  the  use  of  an  Iron  Follower  or  Cap  on  Piles  to  be  Recommended? 
Sam'l  Young.     Eng.  News,  v.  50,  p.  247,  Sept.  17,  1903.       Pile  Driving. 
Eugene  Lentilhon.     Eng.  News,  v.  29,  p.  14,  Jan.  5,  1893.       Cast-Iron 
Shoes  with  Chilled  Points.     Eng.  News,  v.  32,  p.  224,  Sept.  20,  1894. 
Pile  Shoes.     Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1910,  v.  n,  p.  194, 
Part  I.       Pile  Splices.     Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1910,  v.  u, 
p.  192,  Part  I. 

PILE  DRIVING. — Principles  of  Practice.  Manual  Am.  Ry.  Eng.  Assoc. 
Pile  Driving.  S.  E.  Thompson.  Eng.  News,  v.  46,  p.  282,  Oct.  17,  1901; 
Eng.  Rec.,  v.  44,  p.  8,  July  6,  1901.  Pile  Driving.  E.  H.  Bedsler. 
Eng.  News,  v.  16,  p.  83,  August  7,  1886.  Notes  on  Pile  Foundations  in 
Chicago.  Eng.  News,  v.  30,  p.  228,  Sept.  21,  1893.  Some  Instances  of 
Piles  and  Pile  Driving,  New  and  Old.  Horace  J.  Howe.  Jour.  Assoc. 
Eng.  Soc.,  v.  20,  p.  257,  294,  Apr.,  1898.  Notes  on  Pile  Driving.  Jas.  C. 
Hough.  Jour.  Assoc.  Eng.  Soc.,  v.  25,  p.  135,  Sept.,  1900.  Driving 
Piles  in  Dry  Ground.  P.  F.  Barr.  Eng.  News,  v.  52,  p.  545,  Dec.  15, 
1904.  Novel  Method  of  Facilitating  Pile  Driving.  I.  O.  Baker.  Eng. 
News,  v.  57,  576,  May  23,  1907.  Some  Pile-Driving  Experiments  in 
Connection  with  the  Construction  of  the  Charles  River  Dam.  J.  A. 
Holmes.  Engr.-Contr.,  v.  29,  p.  115,  Feb.  19, 1908.  Pile- Driving  Notes. 
J.  E.  Crawford.  Eng.  News,  v.  61,  p.  622,  June  10,  1809.  Supporting 
Power  of  Piles.  E.  P.  Goodrich.  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc., 
1910,  v.  n,  p.  220,  Part  I.  Pile  Driving  Without  Leads.  L.  C.  Lawton. 
Ry.  Age  Gaz.,  v.  53,  p.  no,  June  19,  1912.  Pile  Driving  in  Two  Stages. 

C.  E.  Smith.     Proc.  Am.  Ry.  Eng.  Assoc.,  1913,  v.  14,  p.  238,  Part  II. 
Piles  Driven  with  Butt  Ends  Down.     Ry.  Age  Gaz.,  v.  49,  p.  787.       Con- 
strutting  a  Braced  Pile  Bulkhead.     Eng.  Rec.,  v.  59,  p.  571,  May  i,  1909. 
Method  of  'Spotting'   Foundation  Piles  for  a  Bridge  Pier.     Geo.  A. 
McKay.     Engr.-Contr.,  v.  33,  p.  607,  June  29,  1910.       Cutting  Off  Piles 
by  Dynamite.     Eng.  Rec.,  v.  36,  p.  291,  Sept.  4,  1897.       Durability  of 
Piles  Driven  in  Tidal  Waters  and  Cut  Off  above  Low  Water.    L.  Y. 
Schermerhorn.     Eng.  News,  v.  47,  p.  70,  Jan.  23,  1902.       Screw-jacks 
for  Pulling  Piles.     E.  M.  Malmquist.     Pile-Pulling  Rig  Used  in  Kansas 
City.     Wm.   P.   Parker.     Eng.   News,  v.   49,   p.   348,   April   16,    1903. 
Methods  and  Costs  of  Pile  Pulling  and  Pile  Blasting.     Eng.  News,  v.  49, 


57°         REFERENCES   TO   ENGINEERING   LITERATURE      CHAP.  XIX 

p.  338,  April  16,  1903.  Removing  Piles  by  Blasting.  G.  W.  Stadly 
Eng.  News,  v.  49,  p.  432,  May  14,  1903.  Sawing  Off  Piles  under  Water. 
Eng.  Rec.,v.  50,  p.  437,  Oct.  8,  1904.  New  Portland  Bridge.  H.  A. 
Crafts.  Eng.  Rec.,  v.  53,  p.  252,  Mar.  3,  1906.  Durability  of  Wooden 
Piles.  Concrete  Piles  on  the  Pacific  Coast.  Eng.  Rec.,  v.  53,  p.  525,  Apr. 
28,  1906.  Possibilities  and  Methods  of  Pulling  Steel  Sheet-Piling. 
W.  G.  Fargo.  Engr.-Contr.,  v.  27,  p.  187,  May  i,  1907.  Under-water 
Pile  Saw  with  Guide  Bracket  for  Cutting  to  even  Grade.  Clarence 
Coleman.  Eng.  News,  v.  63,  p.  696,  June  16,  1910.  Clarence  Coleman. 
Engr.-Contr.,  v.  33,  p.  605,  June  29,  1910.  Hand-Operated  Device 
for  Cutting  Off  Submerged  Piles  to  Uniform  Level.  A.  C.  Freeman, 
Engr.-Contr.,  v.  34,  p.  217,  Sept.  7,  1910.  Sawing  Piling  under  Water. 
Ry.  Age  Gaz.,  Jan.  19,  1912,  v.  52,  p.  117.  Old  Piling  Rejuvenated. 
G.  Y.  Skeels.  Eng.  Rec.,  v.  65,  p.  in,  Jan.  27,  1912.  Cost  of  Driving 
Piles.  Eng.  News,  v.  48,  p.  364,  Oct.  30,  1902.  Cost  of  Pile  Driving 
and  Falsework.  Eng.  Rec.,  v.  58,  p.  234,  Aug.  29,  1908.  Notes  on 
Pile-Driving  Costs.  Victor  Windett.  Engr.-Contr.,  v.  35,  p.  709, 
June  21,  1911. 

USE  OF  WATER- JET.— Water-Jet  Pile  Driving,  Lt.  F.  V.  Abbott. 
Annual  Report  Chief  of  Engineers,  U.  S.  A.,  1883,  Part  II,  pp.  1249-1281. 
Chronology  of  the  Water-Jet  as  an  aid  to  Engineering  Construction. 
Eng.  News,  v.  13,  p.  104,  Feb.  14,  1885.  Chronology  of  the  Water-Jet. 
Edwin  Parish.  Eng.  News,  v.  13,  p.  124.  Screen  Dike  and  Jet  Pile- 
Sinking.  Missouri  .River  Commission.  Eng.  News,  v.  24,  p.  498, 
Dec.  6,  1890.  Pile  Driving  by  Water- Jet;  Interstate  Bridge,  Omaha, 
Neb.,  Eng.  News,  v.^i,  p.  316,  April  19,  1894.  Use  of  a  Novel  Water-Jet 
for  Driving  Piles  for  the  Sandy  Hook  Proving  Ground  Railroad  Trestle. 
Sherman  A.  Jubb.  Eng.  News,  v.  53,  p.  456,  May  4,  1905.  Excavation 
and  Pile  Driving  for  Brooklyn  Anchorage  Manhattan  Bridge.  Eng. 
Rec.,  v.  52,  p.  187,  Aug.  12, 1905.  Partial  History  of  the  Use  of  the  Water- 
Jet  in  Sinking  Piles.  Engr.-Contr.,  v.  27,  p.  233,  May  29,  1907.  Water- 
Jet.  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1911,  v.  12,  p.  281.  Use  of 
Water-Jets  in  Pile  Driving.  Eng.  Rec.,  v.  63,  p.  361,  Apr.  i,  1911. 
Refers  to  report  of  Committee  on  Wooden  Bridges  and  Trestles  of  Am. 
Ry.  Eng.  &  M.  W.  Assoc.,  1911,  v.  12,  p.  281. 

OVERDRIVING  PILES. — Examples  of  Overdriving  Piles.  Jas.  W.  Rpllins, 
Jr.  Jour.  Assoc.  Eng.  Soc.,  v.  20,  p.  303,  Apr.,  1898.  Safe  Limit  of  Fall 
in  Driving  Piles.  J.  Y.  Schermerhorn;  G.  W.  Stadly.  Eng.  News,  v.  48, 
p.  294,  Oct.  9,  1902.  Pile  Driving.  Frank  Pidgeon.  Eng.  Rec.,  v.  53, 
p.  465,  Apr.  7,  1906;  Eng.  Rec.,  v.  53,  p.  383,  Mar.  24, 1906.  Overdriven 
Piles.  Eng.  Rec.,  v.  53,  p.  166,  Feb.  10,  1906;  Eng.  Rec.,  v.  53,  p.  192, 
Feb.  17,  1906.  Overdriving  Piles.  Trans.  Am.  Soc.  C.  E.,  v.  69,  p.  104, 
Oct.  1910;  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1909,  v.  10,  p.  572;  1910, 
v.  n,  p.  196;  1911,  v.  12,  p.  281. 


ART.  193  TIMBER   PILES    AND   PILE   DRIVING  571 

CHEMICAL  PRESERVATION  OF  PILES. — Destruction  of  Piles  by  Limnoria 
Lignorum  and  Limnoria  Terebraus  in  Boston  Harbor.  Report  of  Special 
Examination,  fully  illustrated  by  Heliatypes.  Report  of  City  Engineer, 
Boston,  1888,  p.  40.  Creosoted  Piles.  J.  W.  Haugh.  Jour.  Assoc. 
Eng.  Soc.,  v.  25,  p.  137,  Sept.,  1900.  Destruction  of  Creosoted  Piles. 
R.  R.  Gaz.,  v.  40,  p.  531,  May  25,  1906.  Good  and  Bad  Creosoting. 
Ry.  Age  Gaz.,  v.  45,  p.  1270,  Oct.  30,  1908.  More  Evidence  of  the 
Longevity  of  Creosoted  Piles.  W.  G.  Am.  Eng.  News,  v.  61,  p.  277, 
Mar.  n,  1909.  Specifications  for  Creosoting  Piling  at  the  Pacific 
Creosoting  Co.  Eng.  News,  v.  64,  p.  473,  Nov.  3,  1910.  Creosote  Piles 
after  30  Years.  Ry.  Age  Gaz.,  v.  53,  p.  114,  June  19, 1912.  Interesting 
Pile  Failure.  Jno.  W.  Cunningham.  Eng.  News,  v.  70,  p.  465,  Sept.  4, 
1913.  Report  of  Creosoted  Piling  in  Santa  Fe  Galveston  Bay  Bridge. 
F.  B.  Ridgeway.  Proceedings  of  Tenth  Annual  Meeting  of  Am.  Wood 
Preservers'  Assoc.,  Jan.,  1914. 

MECHANICAL  PROTECTION  OF  PILES. — Concrete  and  Pipe  Jacketing  for 
Wooden  Piles.  R.  Montfort.  Eng.  Rec.,  v.  30,  p.  88,  June  7,  1894. 
Teredo-Proof  Sheathing  of  Piles.  Eng.  News,  v.  31,  p.  in,  Feb.  8,  1894. 
Protecting  Piles  against  the  'Teredo  NavaKs'  on  the  Louisville  &  Nashville 
Railroad  Company's  Lines.  R.  Montfort.  Trans.  Am.  Soc.  C.  E.,  v.  31, 
221,  Feb.,  1894.  Form  for  Applying  Concrete  Armoring  to  Timber 
Piles.  Eng.  News,  v.  55,  p.  582,  May  24,  1906.  Reinforced-Concrete 
Casing  for  the  Protection  of  Piles  on  Wharf  Construction.  F.  A.  Koe- 
titz.  Jour.  Assoc.  Eng.  Soc.,  v.  36,  p.  223,  May,  1906.  Protecting  Piles 
from  the  Teredo.  R.  R.  Gaz.,  v.  14,  p.  137,  Aug.  17,  1906.  New  Con- 
crete Covering  for  Timber  Piles  in,  Teredo-Infested  Waters.  Philip 
Aylett.  Eng.  News,  v.  55,  p.  21,  Jan.  4,  1906.  A  Large  Pile  Protection 
Contract.  Eng.  Rec.,  v.  57,  p.  474,  Apr.  4,  1908.  Mechanical  Protec- 
tion of  Piles.  Eng.  News,  v.  60,  p.  in,  June  30,  1908.  Preservation  of 
Piling  against  Maine  Wood  Borers.  C.  Stowell  Smith.  U.  S.  Forest 
Service,  Circular  128,  1908.  Protected  Piles  for  use  in  Teredo-In- 
fested Waters.  Eng.  Rec.,  v.  58,  p.  474,  Oct.  24,  1908.  Timber  Pile 
Protection  in  San  Diego  Bay.  Eng.  Rec.,  v.  57,  p.  174?  Feb.  15,  1908. 
Reinforced-Concrete  Wharf.  Trans.  Am.  Soc.  C.  E.,  v.  66,  p.  289,  Mar., 

1910.  Notes  on  Pile  Protection.     T.   Howard  Barnes.     Jour.  Assoc. 
Eng.  Soc.,  v.  47,  p.  101,  Sept.,  1911.       Concrete  Casings  filled  with  sand 
as   Wooden  Pile  Protection.     .  Thos.    Englehart.     Eng.   News,   v.   66, 
p.  412,  Oct.  5,  1911.      Notes  on  Pile  Protection.     Ry.  Age  Gaz.,  v.  51, 
p.  1345,  Dec.  29,  1911.       Mechanical  Protection  of  Piling  against  Maine 
Wood  Borers.     Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1910,  v.  IT,  p.  200; 

1911,  v.  12,  p.  305.       Covering  Worn  Timber  Piles  with  Cement-Gun 
Concrete.     Eng.  News,  v.  68,  p.  536,  Sept.  19,  1912.       Cement  Gun  for 
Coating  Timber  Piles.     Morton  L.  Tower.     Eng.  News,  v.  68,  p.  723, 
Oct.  17,  1912. 


572         REFERENCES   TO    ENGINEERING   LITERATURE      CHAP.  XIX 

ART.  194.    BEARING  POWER  OF  PILES 

THEORY  AND  PRACTICE. — Formula  for  Bearing  Power.  Supporting 
Povver  of  Piles.  Franz  Kreuter.  Eng.  Rec.,  v.  33,  p.  330,  Apr.  n,  1896; 
New  Formula,  etc.,  Ed.,  p.  343,  Apr.  18.  Supporting  Power  of  Piles. 
Ernest  P.  Goodrich.  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1910,  v.  n, 
p.  217;  Engr.-Contr.,  v.  33,  p.  371,  April  20,  1910.  Ultimate  Load  on 
Pile  Foundations;  a  Static  Theory.  John  H.  Griffith.  Trans.  Am.  Soc. 
C.  E.,  v.  70,  p.  412,  Dec.,  1910.  Formula  for  Bearing  Power  of  Piles. 
H.  B.  Seaman.  Trans.  Am.  Soc.  C.  E.,v.  75,  p.  330,  Dec.,  1912.  Column 
Action  in  Files.  Eng.  News,  v.  60,  p.  18,  July  2,  1908.  Column  Action 
in  Piles;  Stiffening  Piles  by  Riprap.  E.  P.  Goodrich.  Eng.  News,  v.  60, 
p.  41,  July  9,  1908.  Supporting  Power  of  Piles.  Ernest  P.  Goodrich. 
Trans.  Am.  Soc.  C.  E.  v.  48,  p.  180,  Aug.,  1902.  The  Supporting  Power 
of  Piles.  C.  BaiJlairge;  E.  P.  Goodrich.  Eng.  Rec.,  v.  45,  p.  183,  Feb.  22, 
1902.  Formulas  for  Safe  Loads  on  Bearing  Piles.  John  C.  Trautwine, 
Jr.  and  Editor  A.  M.  Wellington.  Eng.  News,  v.  20,  p.  509,  Dec.  29,  1888. 
Uniform  Practice  in  Pile  Driving.  J.  Foster  Crow  ell.  Trans.  Am.  Soc. 
C.  E.,  v.  27,  p.  99,  129,  589,  Aug.  and  Nov.,  1892.  The  discussion  was 
reprinted  in  Eng.  News,  v.  28,  p.  412,  438,  460,  Nov.  3,  10  and  17,  1892. 
Uniform  Practice  in  Pile  Driving.  A.  M.  Wellington.  Eng.  News,  v.  28, 
p.  398,  Oct.  27,  1892.  Safe  Load  for  Bearing  Piles.  A.  M.  Wellington,  v. 
28,  p.  469,  Nov.  17,  1892.  Safe  Load  for  Bearing  Piles.  A.  M.  Welling- 
ton. Eng.  News,  v.  28,  p.  469,  Nov.  17,  1892.  Bearing  Power  of  Piles. 
A.  M.  Wellington.  Eng.  News,  v.  31,  p.  283,  Apr.  5,  1894.  Pile-Driving 
Formulas.  R.  R.  Gaz.,  v.  31,  p.  608,  Sept.  i,  1899.  Engineering  News 
Formula,  Editorial.  Eng.  News,  v.  55,  p.  499,  May  3,  1906.  Analytical 
Investigation  of  the  Resistance  of  Piles  to  Superincumbent  Pressure, 
Deduced  from  the  Force  of  Driving,  with  Application  of  the  Formula  to 
the  Foundation  of  Fort  Montgomery,  Rouse's  Point,  N.  Y.  by  Bvt.  Lt. 
James  L.  Mason,  1850.  Papers  on  Practical  Engineering  No.  5.  Driving 
Piles.  A.  M.  VanAuken.  R.  R.  Gaz.,  v.  19,  p.  507,  Aug.  5, 1887.  Driv- 
ing Piles.  E.  D.  T.  Myers.  R.  R.  Gaz.,  v.  19,  p.  521,  Aug.  12,  1887. 
Diagrams  to  Determine  the  Bearing  Power  of  Piles.  G.  F.  Stickney. 
Eng.  Rec.,  v.  56,  p.  720,  Dec.  28,  1907.  Instructions  regarding  Test 
Piles  on  the  New  York  Barge  Canal.  Eng.  Rec.,  v.  56,  p.  720,  Dec.  28, 
1907.  Diagram  for  Determining  the  Safe  Load  on  Piles.  Arthur  S. 
Milinowski.  Eng.  News,  v.  65,  p.  139,  Feb.  2,  1911.  Pile-Driver 
Diagram.  Eugene  F.  Kriegsman.  Eng.  Rec.  v.  65,  p.  417,  Apr.  13,  1912. 
Diagram  of  Safe  Loads  on  Piles.  Engr.-Contr.,  v.  37,  p.  94,  Jan.  24,  1912. 
Some  Facts  of  Experience  in  Pile  Driving.  W.  B.  W.  Howe  and  A.  M. 
Wellington.  Eng.  News,  v.  28,  p.  543,  Dec.  8,  1892.  Supporting  Power 
of  Piles  Driven  by  a  Steam  Hammer  after  Standing.  Robert  Follansbee. 
Eng.  News,  51,  p.  542,  June  9,  1904.  Anomalous  Pile  Resistance  in  Soft 


ART.  195  CONCRETE   PILES  573 

Mud;  Effect  of  Hammer  Shock.  W.  C.  Hammatt.  Eng.  News,  v.  58,  p. 
173,  Aug.  15,  1907.  Pile  Driving  Factors  of  Safety.  A.  M.  Welling- 
ton, Eng.  News,  v.  21,  p.  313,  Apr.  6,  1889. 

TEST  PILES;  RECORDS;  SPECIFICATIONS. — Lesson  in  Pile  Driving. 
Eng.  News,  v.  22,  p.  368,  Oct.  19,  1889.  Some  Facts  of  Experience  in 
Pile  Driving.  W.  B.  W.  Howe,  A.  M.  Wellington.  Eng.  News,  v.  28, 
p.  543,  Dec.  8,  1892.  Test  Piles.  J.  C.  Trautwine,  Jr.  Trans.  Am. 
Soc.  C.  E.,  v.  27,  p.  148-160,  Aug.,  1892.  Actual  Resisting  of  Bearing 
Piles.  A.  M.  Wellington.  Eng.  News,  v.  29,  p.  171,  Feb.  23,  1893. 
Bearing  Power  of  Piles.  Eng.  News,  v.  30,  p.  3,  July  6,  1893.  Bearing 
Power  of  Piles.  Editorial.  Eng.  News,  v.  31,  p.  283,  Apr.  5,  1894.  Tests 
of  the  Bearing  Power  of  Piles.  Eng.  News,  v.  31,  p.  348,  Apr.  26,  1894. 
Test  Piles.  Jour.  Assoc.  Eng.  Soc.,  v.  20,  p.  269,  271,  283,  312,  Apr.,  1898; 
J.  P.  Carlin,  Eng.  Rec.,  v.  43,  p.  450,  May  n,  1901.  Test  Piles.  E.  P. 
Goodrich.  Trans.  Am.  Soc.  C.  E.,  v.  48,  p.  183,  210,  Aug.,  1902.  Con- 
crete-Pile Wall  Foundations.  Eng.  Rec.,  v.  50,  p.  431,  Oct.  8,  1904. 
Concrete  Pile  Foundation  of  the  U.  S.  Express  Co.  Building,  New  York 
City.  'Eng.  News,  v.  52,  p.  348,  Oct.  20,  1904.  Test  Loads  of  Piles 
Driven  with  a  Steam-Hammer.  J.  J.  Welsh.  p  Eng.  News,  v.  52,  p. 
497,  Dec.  i,  1904.  Test  Piles.  W.  B.  W.  Howe.  Trans.  Am.  Soc. 
C.  E.,  v.  54,  p.  413,  June,  1905.  Applying  a  Load  to  Test  Piles  by  Means 
of  a  Lever.  Dewitt  C.  Webb.  Eng.  News,  v.  65,  p.  172,  Feb.  9,  1911. 
Pile  Record  Forms.  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1910,  v.  IT, 
p.  185;  1911,  v.  12,  p.  278.  Form  for  Pile-Driving  Records  used  on  the 
Norfolk  &  Southern  Ry.  Thos.  W.  Cothran.  Eng.  News,  v.  57,  p.  596, 
May  30,  1907.  Pile-Driving  Records.  Thos.  W.  Cothran.  Eng.  Rec., 
v.  55,  p.  638,  June  i,  1907.  Anothe.  Form  for  Pile-Driving  Records. 
Tyrrell  B.  Shertzer.  Eng.  News,  v.  58,  p.  66,  June  18,  1907.  Pile 
Records.  Eng.  Rec.,  v.  57,  p.  429,  Apr.  4,  1908.  Foundations  of  the 
New  Post-Office  and  Government  Building  at  Chicago.  Eng.,  Rec.,  v.  39, 
p.  66,  Jan.  27,  1898.  Pile  Driving,  Editorial.  Eng.  Rec.,  v.  53,  p.  383, 
Mar.  24,  1906. 

ART.  195.     CONCRETE  PILES 

TYPES  OF  CONCRETE  PILES. — Bulkhead  and  Pier  for-  the  New  Port  of 
San  Diego,  Cal.  Eng.  News,  v.  69,  p.  498,  Mar.  13,  1913.  Comparison 
of  Concrete  and  Timber  Piling  on  Basis  of  Cost.  E.  W.  Gaylord.  Engr.- 
Contr.,  v.  32,  p.  486,  Dec.  8,  1909.  Concrete  Piles.  Proc.  Am.  Ry. 
Eng.  Assoc.,  1910,  v.  n,  p.  203-216.  Concrete  Piles.  Howard  J.  Cole. 
Trans.  Am.  Soc.  C.  E.,  v.  65,  p.  467,  Dec.,  1909.  Reconstruction  of  the 
Atlantic  City  Steel  Pier  in  Reinforced  Concrete.  Eng.  News,  v.  56,  p. 
90,  July  26, 1906.  Shop-made  Reinforced-Concrete  Piles.  L.  J.  Mensch. 
Eng.  News,  v.  60,  p.  620,  Dec.  3,  1908.  Sixth  Street  Viaduct,  Kansas 
City.  E.  E.  Howard.  Trans.  Am.  Soc.  C.  E.,  v.  65,  p.  42,  Dec.,  1909. 


574         REFERENCES    TO   ENGINEERING   LITERATURE      CHAP.  XIX 

Concrete  Piles  used  in  the  Steamship  Terminals  at  Brunswick,  Ga.  and  in 
Navy  Yard  Pier  at  Charleston,  S.  C.     M.  M.  Cannon.    Jour.  Assoc.  Eng. 
Soc,  v.  42,  p.  24,  Jan.,  1909.      Reprinted  in  Eng.  News,  v.  61,  p.  549, 
May  20,  1909;  reprinted  in  Eng.  Rec.,  v.  59,  p.  358,  Mar.  27,  1909.       Pen- 
horn  Creek  R.  R.  Viaduct,  Jersey  City.     Eng.  Rec.,  v.  61,  p.  401,  April  2, 
1910.       Seventh  Street  Viaduct  at  Des  Moines,  la.     Ry.  Age  Gaz.,  v.  53, 
p.  627,  Oct.  4,  1912.       Pennsylvania  Ore  Unloading  Dock  at  Cleveland. 
Ry.  Age  Gaz.,  v.  52,  p.  335,  Feb.  23, 1912;  Eng.  News,v.  67,  p.  320,  Feb.  22, 
1912;  Eng.  Rec.,  v.  65,  p.  199,  212,  Feb.  24,  1912.       Reinforced-Concrete 
Piles  on  the  Chicago,  Rock  Island  and  Pacific  Ry.     Eng.  Rec.,  v.  67,  p. 
606,  May  31,  1913.       Approach  to  Municipal  Bridge,  St.  Louis.     Eng. 
News,  v.  69,  p.  95,  Jan.  16,  1913.       Reinforced-Concrete  Pile  Foundation 
for  the  Lattewan  Building,  Brooklyn,  N.  Y.     Eng.  News,  v.  54,  p.  594, 
Dec.  7,   1905.       Method  of   Manufacturing  Reinforced-Concrete    Piles 
by  Rolling.     Eng.  News,  v.  56,  p.  105,  July  26,  1906.       Description  of 
the  Manufacture  of  the  Chenoweth  Pile.     Eng.  News,  v.  56,  p.   105, 
June  26,  1906.      Use  of  Concrete  Piling  in  the  Boardwalk  at  Atlantic 
City.     Aldrich  Durant.     Ry.  Age  Gaz.,  v.  45,  p.  99,  June  17,   1908. 
Notes  on  the  Design  and  Manufacture  of  Concrete  Piles.     Eng.  Rec.,  v. 
65,  P-  379,  April  6,   1912.     Constructing  a  Concrete  Pile  Foundation. 
Eng.  News,  v.  67,  p.  840,  May  2,  1912.       Concrete  Quay  Wall  on  a  Cora] 
Foundation.     Eng.  Rec.,  v.  66,  p.  526,  Nov.  9,  1912.      Notes  on  the 
Economics  of  Concrete  Pile  Foundation  Work.     Engr.-Contr.,  v.  28,  p. 
297,  Nov.  27,  1907.       Concrete  Pile  Foundations  at  Aurora,  111.     Eng. 
News,  v.  48,  p.  495,  Dec.  n,  1902.       Reinforced-Concrete  Piles  with 
Enlarged  Footings  for  Underpinning   a  Building.     J.   Albert  Holmes. 
Eng.  News,  v.  51,  p.  567,  June  16,  1904.       Concrete  Pile  Foundations  at 
Washington  Barracks,  D.  C.     John  Stephen  Sewell.     Eng.  Rec.,  v.  50, 
p.  360,  Sept.  24,  1904.       Details  of  Concrete  Piling  at  Washington  Bar- 
racks. D.  C.     Eng.  Rec.,  v.  50,  p.  463,  Oct.  15,  1904.       Simplex  System  of 
Concrete  Piling.     Constantine    Sherman.     Proc.    Engr's.    Club,    Phila- 
delphia, v.   22,  p.   347,  October,   1905.       Simplex  System  of  Concrete 
Piling.     Thomas  MacKellar.    Jour.  Assoc.  Eng.  Soc.,  v.  39,  p.  266,  Oct., 
1907.       Concrete  Piles  with   Enlarged   Bases.     Hunley   Abbott.     Eng. 
News,  v.  62,  p.  684,  Dec.  16,  1909.       Fifth  Avenue  Viaduct  at  Seattle. 
Eng.  Rec.,  v.  63,  p.  200,  Feb.  18,  1911.       Concrete  Pile  Footings  for  the  42- 
Story  L.  C.  Smith  Building,  Seattle,  Wash.     Eng.  News,  v.  68,  p.  914.,  Nov. 
14,1912.       Abutment  No.  5  of  .Substructure  of  the  P.  &L.E.  R.R.     Bridge 
over  the  Ohio  River  at  Beaver,  Pa.,  by  A.  R.  Rayner.     Proc.  Eng.  Soc.  W. 
Pa.  v.  26,  p.  16,  Feb.,  1910.    Tests  on  Cast-in- Place  Concrete  Piles.    Fran- 
cis L.  Pruyn.     Eng.  News,  v.  69,  p.  592,  Mar.  20,  1913;  Eng.  Rec.,  v.  67, 
p.  328,  Mar.  22,  1913.       Methods  of  Constructing  and  Driving  Combina- 
tion and  Timber  Piles  with  some  Results  of  Tests.     Engr.-Contr.,  v.  33, 
p.  122,  Feb.  9,  1910.       Concrete  Pipe  Failures.     Causes  and  Remedies. 


ART.  196  METAL   AND    SHEET   PILES  575 

C.  S.  Ho  well.  Eng.  News,  v.  68,  p.  589,  Sept.  26,  1912.  Some  Ex- 
periences with  Concrete  Piles  in  Chicago.  J.  Norman  Jensen.  Eng. 
News,  v.  69,  p.  416,  Feb.  27,  1913. 

DRIVING  CONCRETE  PILES. — Heavy  Hammer  Desirable  for  Driving 
Concrete  Piles.  E.  P.  Goodrich.  Eng.  News,  v.  53,  p.  98,  Jan.  26, 
1905.  Improved  Forms  of  Steam-Pile  Hammers  for  Steel  Sheeting  and 
Concrete  Pile  Work.  J.  R.  Wemlinger.  Engr.-Contr.,  v.  34,  p.  325, 
Oct.  12,  1910.  New  System  of  Concrete  Piles.  W.  P.  Anderson.  Eng. 
Rec.,  v.  50,  p.  494,  Oct.  22,  1904.  Corrugated  Concrete  Foundation 
Piles  for  a  Seven-story  Building.  Eng.  Rec.,  v.  54,  p.  150,  Aug.  n,  1906. 
Concrete  Piles  at  Brunswick,  Ga.,  and  Charleston,  S.  C.  M.  M.  Cannon. 
Jour.  Assoc.  Eng.  Soc.,  v.  42,  p.  24,  Jan.,  1909;  Eng.  News,  v.  61,  p.  549, 
May  20,  1909.  Driving  Concrete  Piles.  Eng.  News,  v.  63,  p.  623, 
May  26,  1910.  Method  of  Jetting  down  Concrete  Piles  and  Records  of 
Output.  Engr.-Contr.,  v.  34,  p.  228,  Sept.  14,  1910.  Concrete  Pile- 
Driving  Practice  on  the  Burlington  Railroad.  L.  J.  Hotchkiss.  Eng. 
Rec.,  v.  64,  p.  258,  Aug.  26,  1911.  Driving  Concrete  Piles  with  a  12  ooo- 
pound  Hammer.  Eng.  Rec.,  v.  64,  p.  763,  Dec.  30,  1911.  Concrete 
Piles  for  Bridge  Foundations.  Ry.  Age  Gaz.,  v.  51,  p.  480,  Sept.  8,  1911. 
Seventh  Street  Viaduct  at  Des  Moines,  Iowa.  Ry.  Age  Gaz.,  v.  53,  p. 
627,  Oct.  4,  1912.  Concrete  Pile  Footings  for  the  L.  C.  Smith  Building, 
Seattle,  Wash.  Eng.  News,  v.  68,  p.  914,  Nov.  14,  1912.  Manufac- 
turing and  Driving  Concrete  Piles.  S.  W.  Bowen.  Eng.  News,  v.  69, 
p.  95,  Jan.  16,  1913.  Concrete  Piles.  Eng.  News,  v.  54,  p.  441,  Oct. 
26,  1905.  Cost  of  Making  and  Placing  Reinforced- Concrete  Piles  at 
Atlantic  City,  N.  J.  Eng.  News,  v.  56,  p.  252,  Sept.  6,  1906.  Cost  of 
Piles  and  Pile  Driving.  S.  E.  Thompson  and  Benjamin  Fox.  Jour. 
Assoc.  Eng.  Soc.,  v.  42,  p.  i,  Jan.,  1909;  Engr.-Contr.,  v.  31,  p.  218, 
Mar.  24,  1909;  Eng.  Rec.,  v.  59,  p.  357,  Mar.  27,  1909.  Municipal 
Bridge  Approach.  ,S.  W.  Bowen.  Eng.  News,  v.  69,  p.  95,  Jan.  16,  1913. 
New  Pile  Formula.  Eng.  Rec.,  v.  65,  p.  248,  Mar.  2,  1912.  Data  and 
Opinions  on  Sustaining  Power  of  Concrete  Piles.  Engr.-Contr.,  v.  32, 
p.  308,  Oct.  13,  1909.  Test  Loading.  E.  E.  Howard.  Trans.  Am.  Soc. 
C.  E.,  v.  65,  p.  61,  Dec.,  1909.  Testing  Piles.  Trans.  Am.  Soc.  C.  E., 
v.  65,  p.  476,  1909.  Value  of  Test  Loading.  Eng.  News,  v.  67,  p.  1229, 
June  27,  1912.  Cast-in-Place  Concrete  Piles.  Irwin  and  Witherow. 
Eng.  Rec.,  v.  67,  p.  591,  May  24,  1913.  Driving  Record  of  Piles  Tested. 
Eng.  News,  v.  70,  p.  555,  Sept.  18,  1913.  Concrete  Pile  Specifications. 
Eng.  Rec.,  v.  68,  p.  581,  Nov.  22,  1913. 

ART.  196.     METAL  AND  SHEET  PILES 

TUBULAR,  DISK,  SCREW,  AND  SAND  PILES. — Foundation  of  Hotel 
Albert,  New  York.  Eng.  Rec.,  v.  51,  p.  293,  Mar.  u,  1900.  Use  of 


576         REFERENCES   TO    ENGINEERING   LITERATURE      CHAP.  XIX 

Pile  Foundations  in  the  East  River  Tunnel  of  the  New  York  Rapid 
Transit  Subway.  Eng.  News,  v.  57,  p.  717,  June  27,  1907.  Experience 
in  Molding  and  Sinking  Concrete  Piles  for  Foundation  Work.  Engr.- 
Contr.,  v.  28,  p.  298,  Nov.  27,  1907.  Special  Foundations  for  a  New 
Edison  Substation.  Eng.  Rec.,  v.  57,  p.  425,  Apr.  4,  1908.  Deep 
Foundation  Construction  in  an  Occupied  Building.  Eng.  Rec.,  v.  61, 
p.  503,  Apr.  9,  1910.  Using  Steel  Foundation  Piles  and  Girders  in  very 
Narrow  Clearance.  Eng.  Rec.,  v.  64,  p.  710,  Dec.,  16,  1911.  Driving 
Steel  Piles  near  Insecure  Foundations.  Eng.  Rec.,  v.  66,  p.  271,  Sept. 
7,  1912.  Action  of  Salt  Water  on  Wrought-Iron  Piles.  Peter  C. 
Haines.  Eng.  News,  v.  19,  p.  143,  Feb.  25,  1888.  Iron  Coal  Pier  at 
Norfolk,  Va.  W.  W.  Coe.  Trans.  Am.  Soc.  C.  E.,  v.  27,  p.  125,  Aug., 
1892.  Iron  Wharf  at  Fort  Monroe,  Va.  John  B.  Duncklee.  Trans. 
Am.  Soc.  C.  E.,  v.  27,  p.  115,  Aug.,  1892.  Hydraulic  Pile-Screwing. 
C.  W.  Anderson.  Eng.  Rec.,  v.  41,  p.  570,  June  16,  1900.  Cienfuegos 
Screw  Pile  Pier.  Eng.  Rec.,  v.  53,  p.  80,  Jan.  20,  1906.  Novel  French 
Method  of  Making  Foundations  in  Soft  Ground.  Eng.  News,  v.  44, 
p.  209,  Sept.  27, 1900.  Compressol  System  of  Making  Concrete  Founda- 
tion. Engr.-Contr.,  v.  28,  p.  220,  Oct.  16,  1907.  Large  Concrete  Piles. 
Win.  F.  Johnston.  Eng.  Rec.,  v.  60,  p.  362,  Sept.  25,  1909. 

TIMBER  SHEET- PILING. — Wooden  Sheet- Piling.  Proc.  Am.  Ry.  Eng. 
&  M.  W.  Assoc.,  1909,  v.  10,  p.  569;  1911,  v.  12,  p.  298.  Wakefield 
Sheet-Piling.  Eng.  News,  v.  53,  p.  331,  Mar.  30,  1905.  Improved 
Scarfed  Point  for  Sheet  Piles.  A.  A.  Parker.  Eng.  News,  v.  55,  p.  609, 
May  31,  1906.  Sheet-Piling  of  Square  Timbers  with  Combined  Guide 
and  Water  Jet  Tube.  Eng.  News,  v.  70,  p.  552,  Sept.  18,  1913. 

STEEL  SHEET-PILING. — Metal  Sheet-Piling  for  Foundations  and  Coffer- 
dams. Eng.  News,  v.  45,  p.  122,  Feb.  14,  1901.  New  Metal  Sheet- 
Piling.  R.  R.  Gaz.,  v.  37,  p.  386,  Sept.  30,  1904.  Behrend  Steel  Sheet- 
Piling.  Eng.  News,  v.  52,  p.  286,  Sept.  29,  1904.  Steel  Sheet-Piling. 
Eng.  News,  v.  54,  p.  545,  Nov.  23,  1905.  Steel  Sheet-Piling  for  Large 
Engine  Foundations.  Eng.  Rec.,  v.  54,  p.  401,  Oct.  13,  1906.  Experi- 
ence with  Steel  Sheet-Piling  in  Hard  Soils.  Wm.  G.  Fargo.  Eng.  News, 
v-  57  P-  374)  Apr.  4,  1907.  Bracing  of  Trenches  and  Tunnels,  with 
Pactical  Formulas  for  Earth  Pressures.  J.  C.  Meem.  Trans.  Am.  Soc.  C  E., 
v.  60,  p.  i,  June,  1908.  Steel  Sheet-Piling  Costs.  Eng.  Rec.,  v.  57,  p.  804, 
June  27,  1908.  Steel  Sheet-Piling  for  Retaining  Earth  under  Spread 
Footings.  Eng.  Rec.,  v.  58,  p.  15,  July  4,  1908.  Steel  Sheet- Piling 
for  a  Short  Trench.  Eng.  Rec.,  v.  58,  p.  40,  July  n,  1908.  Steel  Sheet- 
Piling  for  Pipe-Line  Trench.  Ry.  Age  Gaz.,  v.  45,  p.  430,  July  3,  1908. 
New  Uses  for  Steel.  Ry.  Age  Gaz.,  v.  45,  p.  821,  Aug.  28,  1908.  Devel- 
opment and  Use  of  Steel  Sheet-Piling,  with  some  Data  on  the  Preservation 
of  Steel  Buried  in  the  Ground.  J.  R.  Wemlinger.  Engr.-Contr.,  v.  31, 
p.  406,  May  19,  1909.  Steel  Sheeting  and  Steel-Piling.  L.  R.  Gifford. 


ART.,iQ7  COFFERDAMS  577 

Trans.  Am.  Soc.  C.  E.,  v.  64,  p.  441,  Sept.,  1909.  Principal  Types  of  Steel 
Sheet-Piling.  Proc.  Am.  Ry.  Eng.  &  M.  W.  Assoc.,  1909,  v.  10,  p.  570. 
Hand-Driven  Steel  Sheet-Piling,  Bush  Terminal,  Brooklyn.  Eng.  Rec., 
v.  62,  p.  209,  Aug.  20,  1910.  Chisel  Point  for  Driving  Steel  Sheet-Piling. 
H.  M.  Morse.  Eng.  Rec.,  v.  66,  p.  704,  Dec.  21,  1912.  Foundations 
for  the  Tunkhannock  Viaduct.  Eng.  Rec.,  v.  67,  p.  484,  May  3,  1913. 

OTHER  TOPICS. — Brooklyn  Tunnel  of  the  New  York  Rapid  Transit 
Railroad.  Driving  Sheet-Piling.  Eng.  Rec.,  v.  48,  p.  530,  Oct.  30,  1903. 
Methods  and  Cost  of  Operating  Pile-Drivers  and  of  Driving  Steel  Sheet- 
Piling.  Engr.-Contr.,  v.  27,  p.  193,  May  i,  1907.  Some  Suggestions 
on  Methods  of  Driving,  Cutting  and  Pulling  Steel  Sheet  Piles  with  Figures 
of  Cost.  R.  B.  Woodworth.  Engr.-Contr.,  v.  32,  p.  296,  Oct.  6,  1909. 
Safeguarding  Wall  Foundations  by  Sheet-Piling.  Eng.  Rec.,  v.  64,  p. 
412,  Oct.  7,  1911.  Test  of  Driving  Steel  Sheet-Piling,  Cleveland,  0. 
Engr.-Contr.,  v.  37,  p.  721,  June  26,  1912.  Costs  of  Driving  Steel  Sheet- 
Piling  on  45  jobs.  Engr.-Contr.,  v.  38,  p.  196,  Aug.  14,  1912.  Cost  of 
Driving  Steel  Sheet-Piling  by  a  Novel  Method.  J.  R.  Wemlinger. 
Engr.-Contr.,  v.  38,  p.  395,  Oct.  9,  1912.  Bracing  Trenches  and  Tunnels. 
Eng.  Rec.,  v.  56,  p.  494,  Nov.  2,  1907.  Sheet-Piling  and  Earth  Pressure. 
Eng.  Rec.,  v.  56,  p.  608,  Nov.  30,  1907. 

ART.  197.     COFFERDAMS 

EARTH  COFFERDAMS. — Cofferdams  of  Cement  Bags  Half  Filled  with 
Sand.  Eng.  Rec.,  v.  64,  p.  82,  June  15,  1911.  Clay  Cofferdam.  Eng. 
Rec.,  v.  57,  p.  460,  April  4,  1908.  Earth  Cofferdam  for  West  Neebish 
Channel  of  the  St.  Mary's  River.  Eng.  Rec.,  v.  56,  p.  113,  Aug.  3,  1907. 
Cofferdam  made  of  Fascines.  Eng.  Rec.,  v.  49,  p.  189,  Feb.  13,  1904. 
Earth  Cofferdams.  Eng.  News,  v.  24,  p.  413,  Nov.  8,  1890.  Cofferdam 
for  Dam  No.  48,  Ohio  River.  Eng.  Rec.,  v.  67,  p.  412,  April  12,  1913. 

WOODEN  SHEET- PILE  COFFERDAMS  WITH  GUIDE  PILES. — Cofferdams  for 
Charles  River  Dam,  Boston.  Eng.  Rec.,  v.  53,  p.  300,  Mar.  3,  1906; 
Eng.  News,  v.  53,  p.  31,  Jan.  12,  1905;  Eng.  News,  v.  55,  p.  244,  Mar.  i, 
1906.  Repairing  a  Leaking  Cofferdam.  Eng.  News,  v.  46,  p.  187, 
Sept.  19,  1901.  Cofferdam  Enclosing  the  Thirty- ninth  Street  Sewage 
Pumping  Station,  Chicago.  Eng.  Rec.,  v.  52,  p.  580,  Nov.  18,  1905; 
Eng.  News,  v.  50,  p.  546,  Dec.  17,  1903.  Cofferdam  for  Cambridge 
Bridge.  Eng.  News,  v.  46,  p.  283,  Oct.  17,  1901;  Eng.  Rec.,  V;  51,  p.  52, 
Jan.  14,  1905.  Cofferdams  for  the  Gilbertsville  Bridge  Piers.  Eng. 
Rec.,  v.  51.,  p.  265,  Mar.  4,  1905;  Eng.  Rec.,  v.  51,  p.  570,  May  20,  1905. 
Large  Sheet-Pile  Cofferdam.  Eng.  Rec.,  v.  50,  p.  636,  Nov.  26,  1904. 
Cofferdams  for  Six  Lift  Bridges.  Eng.  Rec.,  v.  57,  p.  39,  Jan.  n,  1908. 
Deep  Cofferdam  for  Key  ham  Dockyard  Extension.  Proc.  Inst.  of  Civ. 
Engrs.,  Dec.  17,  1907. 
37 


578  REFERENCES    TO    ENGINEERING    LITERATURE    CHAP. .XIX 

WOODEN  SHEET-PILE  COFFERDAMS  ON  FRAMES. — Cofferdam  for  Mare 
Island  Dry  Dock  No.  2.  Eng.  Rec.,  v.  57,  p.  428,  April  4,  1908.  Coffer- 
dam for  Pier  at  Kilbourne,  Wis.  Eng.  News,  v.  53,  p.  330,  Mar.  30,  1905; 
R.  R.  Gaz.,  v.  38,  p.  258,  Mar.  17,  1905.  Some  Lessons  from  a  Coffer- 
dam. Eng.  Rec.,  v.  57,  p.  243,  Feb.  29,  1908.  Cofferdams  for  Potomac 
River  Highway  Bridge,  Washington,  D.  C.  Eng.  Rec.,  v.  53,  p.  103, 
Jan.  27.  1906.  Cofferdams  for  Piers  of  the  Chattahoochee  River  Viaduct. 
Eng.  Rec.,  v.  58,  p.  233,  Aug.  29,  1908.  Cofferdam  for  Concrete  Bridge 
at  Goat  Island.  Eng.  Rec.,  v.  43,  p.  147,  Feb.  16,  1901.  Cofferdams  for 
Kentucky  and  Indiana  Railway  Bridge.  Ry.  Age  Gaz.,  v.  51,  p.  210, 
Aug.  4,  1911.  Cofferdam  for  P.  B.  &  W.  R.  R.  at  Wilmington,  Del. 
Proc.  Engrs.  Club,  Phila.-,  1908,  v.  25,  p.  333. 

WOODEN  SHEET-PILE  COFFERDAMS  ON  CRIBS. — Heavy  Cofferdam 
Construction  at  Niagara  Falls.  Trans.  Can.  Soc.  C.  E.,  v.  19,  p.  62,  1905; 
Eng.  Rec.,  v.  49,  p.  180,  Feb.  13,  1904;  Eng.  News,  v.  54,  p.  561,  Nov.  30, 

1905.  Cofferdam  for  Pier  No.  4  of  the  Aqueduct  Bridge,  Georgetown, 
D.  C.     Eng.  Rec.,  v.  44,  p.  125,  Aug.  10,  1901.       Cofferdam  for  Great 
Kanawha  Dam.     Eng.  News,  v.  36,  p.  98,  Aug.  13,  1896.       Cofferdam 
for  Hydro-Electric  Development  at  Kilbourne,  Wis.     Eng.  Rec.,  v.  60, 
p.  321,  Sept.  1 8,  1909.       Cofferdam  Construction  of  the  Hydro-Electric 
Plant  of  the  Rockingham  Power  Company.  Rockingham,  N.  C.     Eng. 
Rec.,  v.  57,  p.  423,  April  4,  1908.       Cofferdam  Excavation  for  a  Power 
Station.     Eng.  Rec.,  v.  57,  p.  92,  Jan.  25,  1908.       Cofferdam  Construc- 
tion for  the  Neals  Shoals  Power  Plant.     Eng.  Rec.,  v.  53,  p.  272,  Mar.  3, 

1906.  Cofferdam  Construction  for  Spier  Falls  Dam.     Eng.  Rec.,  v. 
47,  p.  689,  June  27,  1903.       No  sheet-piling  was  used  in  this  work,  a  fill 
of  stones  being  made  on  the  upstream  face  of  the  dam,  and  over  this  a 
heavy  gravel  fill  was  placed.     Cofferdam  Construction  of  the  Connecticut 
River  Power  Co.     Eng.  Rec.,  v.  59,  p.  443,  April  3,  1909.       Cofferdam 
Construction  of  the  Holler  Dam.     Eng.  Rec.,  v.  62,  p.  480,  Oct.  29,  1910. 
Plan  for  Building  Cofferdams  for  River  Piers.     Eng.  News,  v.  56,  p.  560, 
Nov.  29,  1906. 

STEEL  SHEET-PILE  COFFERDAMS. — Cofferdams  of  a  Chicago  Bridge. 
Eng.  Rec.,  v.  49,  p.  413,  April  2,  1904.  On  guide  piles.  Cofferdam 
Construction  for  the  Substructure  of  a  Swing  Bridge.  Eng.  Rec.,  v.  67, 
p.  268,  Mar.  8,  1903.  Steel  sheet  piles  with  guide  piles.  Steel  Sheet- 
Pile  Cofferdam  at  Power-House  Intakes  at  Omaha.  Eng.  Rec.,  v.  59, 
p.  17,  Jan.  2,  1909.  On  frames.  Steel  Sheet-Piling  for  Bridge  Pier 
Cofferdams.  Eng.  Rec.,  v.  55,  p.  246,  Mar.  2,  1907.  On  frames. 
Steel  Sheet-Pile  Cofferdam  for  a  Ship  Lock  at  Buffalo,  N.  Y.  Eng.  News, 
v.  60,  p.  394,  Oct.  8,  1908;  Eng.  Rec.,  v.  57,  p.  747,  June  13,  1908;  Eng. 
Rec.,  v.  59,  p.  385,  April  3,  1909;  Bulletin  No.  103,  Lackawanna  Steel  Co. 
Tunkhannock  Viaduct  Cofferdams.  Eng.  Rec.,  v.  67,  p.  485,  May  3, 
1913.  On  frames.  Steel  Sheet-Pile  Cofferdam  for  Bridge  Piers  over  the 


ART.  197  COFFERDAMS  579 

Cuivre  River  at  Moscow  Mills.  Eng.  Rec.,  v.  49,  p.  557,  April  30,  1904. 
Steel-Piling  Cofferdams  for  Bridge  Piers.  Eng.  Rec.,  v.  53,  p.  505,  April 
21,  1906.  On  frames.  Interesting  cost  data.  Large  Cofferdam  Built 
with  Steel  Sheet-Piling.  Eng.  News,  v.  66,  p.  330,  Sept.  21,  1911;  Eng. 
News,  v.  67,  p.  340,  Feb.  22,  1912.  Cofferdam  Construction  for  Raising 
the  United  States  Battleship  Maine.  Bulletin  No.  102,  Lackawanna 
Steel  Co.;  Eng.  News,  v.  64,  p.  424,  Oct.  20,  1910.  Steel  Sheet-Pile 
Cofferdam  for  Kaw  River  Bridge  Piers.  Eng.  Rec.,  v.  67,  p.  435,  Apr. 
19,  1913.  On  frames. 

CRIB  COFFERDAMS. — Cofferdam  for  New  Inlet  Tower  of  the  St.  Louis 
Water  Works.  Eng.  News,  v.  26,  p.  4,  July  4,  1891.  Crib  Cofferdam 
for  Arthur  Kill  Bridge.  Trans.  Am.  Soc.  C.  E.,  v.  27,  p.  475,  Oct.,  1892. 
Methods  of  Depositing  Concrete  Under  Water.  Report  of  Committee 
on  Masonry.  Proc.  Am.  Ry.  Eng.  Assoc.,  1912,  v.  13,  pp.  487-502. 

MOVABLE  COFFERDAMS. — Movable  Cofferdam  for  Rest  Pier  of  the 
Kinzie  Street  Drawbridge,  Chicago.  Eng.  News,  v.  64,  p.  562,  Nov. 
24,  1910.  Removable  sides  on  grillage.  Movable  Cofferdam  Con- 
struction for  Pequonnock  River  Bridge.  Eng.  Rec.,  v.  50,  p.  127,  July 
30,  1904.  Removable  sides  on  grillage.  Movable  Cofferdams  for 
Bellevue  Boiler  House  Foundations.  Eng.  Rec.,  v.  64,  p.  421,  Oct.  7, 
1911.  Removable  sides  on  grillage.  Cofferdam  with  Removable 
Sides  on  Grillage.  Eng.  News,  v.  43,  p.  217  (see  inset),  Jan.  n,  1900. 
Cofferdams  for  the  Hackensack  River  Bridge  Piers.  Eng.  Rec.,  v.  63, 
p.  224,  Feb.  25,  1911.  Removable  sides  on  grillage.  Cofferdam  for 
Cape  Cod  Canal  Bridge.  Eng.  Rec.,  v.  63,  p.  288,  Mar.  18,  1911.  Re- 
movable sides  on  grillage.  Circular  Cofferdam  for  Highway  Bridge 
Pier  across  the  Passaic  River,  Newark,  N.  J.  Eng.  Rec.,  v.  67,  p.  268, 
Mar.  8,  1913.  Removable  sides  on  grillage.  Cofferdams  for  Queens' 
Bridge,  Melbourne,  Australia.  Eng.  News,  v.  33,  p.  230,  April  4,  1895. 
Movable  cofferdam.  Cofferdam  for  Falls  of  Schuylkill  Bridge.  Eng. 
News,  v.  31,  p.  423,  May  24,  1894;  Proc.  Engrs.  Club,  Phila.,  v.  12,  p.  163, 
May,  1895.  Movable  cofferdam.  Cofferdams  for  Florida  East  Coast 
Railroad  Piers.  Eng.  Rec.,  v.  54,  p.  424,  Oct.  20,  1906.  Movable 
cofferdam. 

MISCELLANEOUS  COFFERDAMS. — Use  of  Canvas  in  Water-tight  Bulk- 
heads. Trans.  Am.  Soc.  C.  E.,  v.  31,  p.  524,  May,  1894.  'A-Frame' 
Cofferdams.  Eng.  Rec.,  v.  66,  p.  374,  Oct.  5,  1912.  Cofferdam  Con- 
struction for  Dearborn  Street  Bridge,  Chicago.  Eng.  Rec.,  v.  56,  p.  278, 
Sept.  14,  1907.  Combination  of  wood  and  steel  sheet-piling.  Cofferdam 
Construction  for  Enlarging  Lachine  Bridge  Piers.  Eng.  Rec.,  v.  63,  p. 
84,  Jan.  21,  1913.  Combination  of  crib  and  sheet-pile  cofferdam.  Cof- 
ferdam for  Bridge  Piers  in  Maine.  Eng.  News,  v.  37,  p.  327  ,May  27, 
1897.  Cofferdam  sunk  through  ice.  Metal  Cylinder  Cofferdam.  Eng. 


580         REFERENCES    TO    ENGINEERING   LITERATURE      CHAP.  XIX 

News,  v.  64,  p.  25,  July  7,  1910.  Cofferdams  with  Water-Tight  Linings. 
Memoires  de  la  Societe  des  Ingenieurs  Civils  de  France,  1900,  p.  472; 
Proc.  Inst.  C.  E.,  v.  144,  p.  347,  1900-01.  Cofferdam  in  Reinforced 
Concrete.  Revue  Technique,  Paris,  v.  26,  p.  226;  Proc.  Inst.  C.  E.,  v. 
163,  p.  409,  1905-06.  Freezing  Process  as  Applied  to  Cofferdams. 
Revue  Technique,  Paris,  v.  26,  p.  57;  Proc.  Inst.  C.  E.,  v.  163,  1905-06. 
p.  408.  Cofferdam  Construction  for  the  Periyar  Dam,  S.  India.  Eng. 
News,  v.  46,  p.  300,  Oct.  24,  1901. 

GENERAL  ARTICLES  ON  COFFERDAMS. — Construction  of  Cofferdams  by 
Thomas  P.  Roberts.  Eng.  News,  v.  54,  p.  138,  Aug.  10,  1905.  Gives 
interesting  personal  experiences.  Experience  with  Steel  Sheet-Piling 
in  Hard  Soils.  Eng.  Rec.,  v.  55,  p.  175,  Feb.  16,  1907.  Economy  of 
Steel  Sheet- Piling  for  Cofferdams.  Eng.  Rec.,  v.  53,  p.  557,  May  5, 
1906.  Construction  of  Cofferdams.  Eng.  Rec.,  v.  65,  p.  244,  Mar.  2, 
1912.  Recent  Practice  in  Cofferdam  Work.  Reports  of  committee 
and  discussions.  Proc.  Assoc.  Ry.  Supts.  Bridges  and  Bldgs.,  1901, 
v.  n,  p.  45;  1906,  v.  16,  p.  92;  1907,  v.  17,  p.  89;  1908,  v.  18,  p.  201. 

ART.  198.    Box  AND  OPEN  CAISSONS 

Box  CAISSONS. — Box  Caissons  of  Wood.  Trans.  Am.  Soc.  C.  E.,  v.  29, 
p.  634,  Sept.,  1893.  Circular  Box  Caisson.  Eng.  Rec.,  v.  64,  p.  720, 
Dec.  16,  1911.  Timber  Crib  Caissons  for  a  Break  Water.  Eng.  News, 
v.  40,  p.  50,  July  28,  1898.  Reinforced-Concrete  Box  Caissons  for  a 
Break  Water.  Eng.  News,  v.  60,  p.  421,  Oct.  15,  1908;  Eng.  News,  v. 
62,  p.  34,  July  8,  1909.  Reinforced-Concrete  Caisson  at  Glen  Cove, 
N.  Y.  Trans.  Am.  Soc.  C.  E.,  v.  70,  p.  450,  Dec.,  1910.  Sinking  a 
Foundation  Caisson  with  Post-Hole  Augers.  Eng.  Rec.,  v.  52,  p.  570, 
Nov.  1 8,  1905.  Sinking  Machinery  Foundations  in  Quicksand  without 
Excavation.  Eng.  Rec.,  v.  52,  p.  526,  Nov.  4,  1905. 

SINGLE-WALL  OPEN  CAISSONS. — Single-Wall  Open  Caissons  for  the 
French  River  Bridge.  Eng.  Rec.,  v.  59,  p.  118,  Jan.  13,  1909;  Trans.  Can. 
Soc.  C.  E.,  v.  22,  p.  204  (see  Plate  20),  1908.  Single-Wall  Open  Caissons 
of  the  Columbia  River  Bridge.  Eng.  News,  v.  66,  p.  392,  Oct.  5,  1911. 
Single-Wall  Open  Caissons  of  the  Fraser  River  Bridge.  Eng.  Rec.,  v.  49, 
p.  679,  May  28,  1904.  Caisson  Construction  Rio  Conchos  Bridge  of 
the  Kansas  City,  Mexico  and  Orient  R.  R.  Ry.  Age  Gaz.,  v.  46,  p.  164, 
Jan.  22,  1909.  Caisson  Construction  for  the  Pivot  Pier  of  the  Coteau 
Bridge.  Eng.  News,  v.  26,  p.  524,  May  30,  1891;  Fowler's  Sub-aqueous 
Foundations,  p.  45.  Caisson  Construction  on  the  Atchison,  Topeka 
and  Santa  Fe  Railway.  Eng.  Rec.,  v.  66,  p.  52,  July  13,  1912.  Draw 
Foundation  of  the  Charlestown  Bridge,  Boston.  Eng.  Rec.,  v.  38,  p. 
186,  July  30,^1898.  Pivot  Pier  Foundation  of  the  Chelsea  Bridge 
North,  Boston.  Eng.  Rec.,  v.  68,  p.  138,  Aug.  2,  1913. 


ART.  198  BOX  AND   OPEN   CAISSONS  581 

CYLINDER  CAISSONS. — New  Chittravati  Bridge  Caissons.  Proc.  Inst. 
C.  E.,  v.  103,  p.  135,  Dec.  9,  1890.  Masonry  caissons.  Field  Engineer- 
ing Abroad.-  Eng.  Rec.,  v.  35,  p.  246,  Feb.  20,  1897.  General  description 
of  caisson  sinking  in  the  far  east.  Sinking  Cylinder  Caissons  with 
Hydraulic  Jacks.  Eng.  Rec.,  v.  56,  p.  454,  Oct.  26,  1907.  Cast-iron 
cylinders  4  feet  in  diameter.  Cylinder  Caissons  for  the  California  City 
Point  Coal  Pier.  Eng.  Rec.,  v.  57,  p.  800,  June  27,  1908.  Cast-iron 
cylinders,  4  feet  in  diameter.  Cylinder  Caissons  for  a  Highway  Bridge 
over  the  Kansas  River  at  Fort  Riley,  Kansas.  Eng.  Rec.,  v.  58,  p.  75, 
July  18,  1908.  Steel  cylinders  5  feet  in  diameter.  Cylinder  Caissons 
for  Bridge  Piers  at  North  Hampton,  Mass.  Eng.  Rec.,  v.  42,  p.  523, 
Dec.  i,  1900.  Steel  cylinders  10  feet  in  diameter.  Cylinder  Caisson 
Construction  on  the  Chicago  and  Northwestern  Ry.  Eng.  News,  v.  68, 
p.  748,  Oct.  24,  1912.  A  valuable  article  describing  a  number  of  instances 
where  cylinder  caissons  were  used.  Cylinder  Caisson  Construction  in 
India.  Eng.  News,  v.  34,  p.  143,  Aug.  29,  1895.  Cylinder  Caisson 
Construction  for  the  Omaha  Interstate  Bridge.  Eng.  Rec.,  v.  47,  p.  98, 
Jan.  24,  1903;  Eng.  Rec.,  v.  29,  p.  218,  Mar.  3,  1894;  Eng.  News,  v.  30, 
p.  410,  Nov.  23,  1893.  Double-shell  caisson,  40  feet  outside  diameter. 
Cylinder  Caisson. Sinking  for  the  Koyakhai  Bridge,  Bengal-Nagpur  Ry. 
Proc.  Inst.  C.  E.,  v.  145,  p.  292,  1900-01;  Eng.  News,  v.  46,  p.  493,  Dec. 
26,  1901.  External  diameter  equals  26^  feet  and  diameter  of  well 
equals  13!  feet.  Cylinder  Caisson  Construction  for  the  Pyrmont 
Bridge,  Sidney,  N.  S.  W.  Proc.  Inst.  C.  E.,  v.  170,  p.  138, 1907.  Caisson 
42  feet  in  external  diameter  and  32  feet  in  internal  diameter.  Caisson 
Construction  for  the  Curzon  Bridge  at  Allahabad.  Proc.  Inst.  C.  E.,  v. 
174,  p.  i,  1907-08.  Caisson  Construction  for  the  Netravati  Bridge  at 
Mangalore.  Proc.  Inst.  C.  E.,  v.  174,  p.  41,  1907-08.  Cylinder  Cais- 
sons of  the  Penhorn  Creek  Viaduct.  Eng.  News,  v.  64,  p.  380,  Oct.  13, 
1910;  Eng.  Rec.,  v.  61,  p.  401,  Apr.  2,  1910.  Caissons  of  reinforced  con- 
crete. Cylinder  Caissons  for  Pier  No.  8,  at  the  Puget  Sound  Navy 
Yard.  Eng.  Rec.,  v.  65,  p.  683,  June  22,  1912.  Caissons  of  reinforced 
concrete.  Cylinder  Caissons  for  the  Lumber  Dock  at  Balboa,  Canal 
Zone.  Eng.  Rec.,  v.  66,  p.  60,  July  20,  1912.  Caissons  of  reinforced 
concrete. 

OPEN  CAISSONS  WITH  DREDGING  WELLS. — Open  Caissons  for  the 
Poughkeepsie  Bridge.  Trans.  Am.  Soc.  C.  E.,  v.  18,  p.  199,  June,  1888; 
Eng.  News,  v.  18,  p.  306.  Open  Caissons  for  the  Copper  River  Bridge. 
Eng.  Rec.,  v.  61,  p.  642,  May  14,  1910.  Timber  caissons.  Open 
Caissons  for  the  Fraser  River  Bridge.  Eng.  Rec.,  v.  49,  p.  679,  May  28, 
1904;  Eng.  News,  v.  53,  p.  612,  June  15,  1905.  Timber  caissons.  Open 
Caissons  for  the  Willamette  Bridge.  Ry.  Age  Gaz.,  v.  51,  p.  81,  July  14, 
1911.  Open  Caissons  for  the  Hawkesburg  Bridge.  Eng.  News,  v.  15, 
p.  98,  Feb.  13,  1886;  Eng.  News,  v.  21,  p.  3,  Jan.  5,  1889;  Eng.  News,  v.  23, 


582         REFERENCES   TO    ENGINEERING   LITERATURE      CHAP.  XIX 

p.  114,  Feb.  i,  1890;  Pattern's  A  Practical  Treatise  on  Foundations, 
p.  268.  Metal  caissons.  Open  Caissons  for  the  Dufferin  Bridge  over 
the  Ganges  River  at  Benares.  Proc.  Inst.  C.  E.,  v.  101,  p.  13,  1889-90. 
Metal  caissons.  Open  Caissons  for  the  Black  Friars  New  Railway 
Bridge.  Proc.  Inst.  C.  E.,  v.  101,  p.  26,  1889-90.  Metal  caissons. 
Open  Caissons  for  the  Hooghly  Bridge.  Proc.  Inst.  C.  E.,  v.  92,  p.  75, 
1887-88.  Metal  caissons.  Open  Caissons  for  a  Railway  Bridge, 
Fitzroy  River  at  Rockhampton,  Queensland.  Proc.  Inst.  C.  E.,  v.  144^ 
p.  45,  1900-01.  Metal  caissons.  Open  Caissons  for  the  Beaver  Bridge 
Piers.  Eng.  News,  v.  63,  p.  509,  May  5,  1910;  Eng.  Rec.,  v.  60,  p.  299, 
Sept.  n,  1909;  Bulletin  No.  i,  Apr.  1909,  by  the  Dravo  Contracting  Co. 
Reinfcrced-concrete  caissons.  Open-Caisson  Construction  for  the  Amer- 
ican River  Bridge.  Eng.  Rec.,  v.  62,  p.  232,  Aug.  27,  1910.  Reinforced- 
concrete  caissons.  Open'Caisson  Construction  for  the  North  Side 
Point  Bridge.  Eng.  News,  v.68,  p.  706,  Oct.  17,  1912.  Reinforced- 
concrete  caissons. 

ART.  199.     PNEUMATIC  CAISSONS  FOR  BRIDGES 

GENERAL. — Pneumatic  Caissons.  R.  R.  Age  Gaz.,  v.  45,  p.  671,  Aug.  7, 
1908;  R.  R.  Age  Gaz.,  v.  45,  p.  703,  Aug.  14,  1908.  Hughes  Air-Lock, 
Valparaiso  Harbor.  Eng.  News,  v.  40,  p.  363,  Dec.  8,  1898.  Special 
Materials  Air-Lock.  Eng.  Rec.,  v.  29,  p.  170,  Feb.  10,  1894.  The  Use 
of  Compressed  Air  in  Tubular  Foundations.  Trans.  Am.  Soc.  C.  E.,  v. 
7,  p.  287,  1878.  Description  of  the  Plenum  Pneumatic  Process  as  Ap- 
plied in  Founding  the  Piers  of  the  St.  Louis  Bridge.  Milnor  Roberts. 
Trans.  Am.  Soc.  C.  E.,  v.  i,  p.  259,  1872.  Bridge  Foundations  in  the 
Columbia  and  Willamette  Rivers  near  Portland,  Ore.  Ralph  Modjeski. 
Jour.  Assoc.  Eng.  Soc.,  v.  49,  p.  43,  Sept.,  1912.  Pneumatic  Caisson 
Work  in  Great  Britain.  Eng.  Rec.,  v.  59,  p.  563,  May  i,  1909.  Lower- 
ing Large  Pneumatic  Caissons.  Eng.  Rec.,  v.  56,  p.  566,  Nov.  23,  1907. 
Reconstruction  of  Coteau  Bridge.  Eng.  Rec.,  v.  62,  p.  628,  Dec.  3,  1910. 
Reinforced-Concrete  Caissons.  Ry.  Age  Gaz.,  v.  47,  p.  492,  Sept.  17, 
1909.  Reinforced-Concrete  Caissons.  Eng.  Rec.,  v.  64,  p.  238,  Aug. 
26,  1911.  North  Side  Point  Bridge,  Pittsburgh.  Eng.  News,  v.  68,  p. 
706,  Oct.  17,  1912. 

WOODEN  CAISSONS.— Pneumatic  Caissons  of  the  Sixth  Street  Viaduct, 
Kansas  City.  Proc.  Am.  Soc.  C.  E.,  v.  35,  p.  81,  Feb.,  1909.  Williams- 
burgh  or  New  East  River  Bridge  Foundations.  Eng.  Rec.,  v.  36,  p.  491, 
Nov.  6,  1897;  Eng.  Rec.,  v.  37,  p.  207,  Feb.  5,  1898,  Eng.  Rec.,  v.  35,  p. 
554,  May  29,  1897;  Eng.  Rec.,  v.  39,  p.  419,  Dec.  17,  1898;  Eng.  Rec.,  v. 
39,  p.  71,  Dec.  24,  1898;  Eng.  Rec.,  v.  39,  p.  397,  Apr.  i,  1899;  Eng.  News, 
v.  37,  p.  331,  May  27,  1897.  Construction  of  Pneumatic  Caissons  for 
the  St.  Louis  Bridge.  Woodward's,  The  St.  Louis  Bridge;  Baker's, 


ART.  199  PNEUMATIC    CAISSONS   FOR   BRIDGES  583 

"Masonry  Construction."  Pneumatic  Caissons  for  the  Third  East 
River  (Manhattan)  Bridge,  New  York.  Eng.  News,  v.  48,  p.  455,  Nov. 
27,  1902;  Eng.  News,  v.  45,  p.  171,  Mar.  7,  1901;  Eng.  Rec.,  v.  43,  p. 
194,  Mar.  2,  1901;  Eng.  Rec.,  v.  46,  p.  510,  Nov.  29,  1902;  Eng.  Rec.,  v. 
49 >  P-  332,  Mar.  12,  1904.  Pneumatic  Caissons  of  the  Cairo  Bridge. 
Morison's,  "The  Cairo  Bridge";  Eng.  News,  v.  25,  p.  122,  Feb.  7,  1891; 
Jour.  Assoc.  Eng.  Soc.,  v.  9,  p.  290,  June,  1890.  Pneumatic  Caissons  of 
the  Memphis  Bridge.  Morison's,  "The  Memphis  Bridge";  Eng.  News, 
v.  30,  p.  509,  Dec.  28,  1893.  Incidents  in  the  Construction  of  the 
Miles  Glacier  Bridge.  Eng.  Rec.,  v.  62,  p.  763,  Dec.  31,  1910.  New 
Cornwall  Bridge  Piers.  Eng.  Rec.,  v.  40,  p.  643,  Dec.  9,  1899.  Quebec 
Bridge  Piers.  Eng.  Rec.,  v.  44,  p.  74,  July  27,  1901.  Monongahela 
Bridge  at  Pittsburgh.  Eng.  Rec.,  v.  47,  p.  2,  Jan.  3,  1903.  Omaha 
Interstate  Bridge.  Eng.  Rec.,  v.  47,  p.  98,  Jan.  24,  1903.  Tower  Foun- 
dations of  the  Manhattan  Bridge.  Eng.  Rec.,  v. 49,  p.  332,  Mar.  12, 1904. 
State  Bridge  at  Hartford,  Conn.  Eng.  Rec.,  v.  50,  p.  764,  Dec.  31,  1904. 
Substructures  of  Bridges  on  the  Spokane,  Portland  &  Seattle  Railway. 
Eng.  Rec.,  v.  58,  p.  555,  Nov.  14,  1908.  Passyunk  Avenue  Bridge 
Piers.  Eng.  Rec.,  v.  61,  p.  388,  Apr.  2,  1910.  Pneumatic  Caisson  Piers 
in  Alaska.  Eng.  Rec.,  v.  61,  p.  559,  Apr.  23,  1910.  St.  Louis 
Municipal  Bridge  Substructure.  Eng.  Rec.,  v.  62,  p.  427,  Oct.  15, 
1910;  Eng.  News,  v.  65,  p.  320,  Mar.  16,  1911.  New  Quebec 
Bridge.  Eng.  Rec.,  v.  62,  p.  372,  Oct.  i,  1910;  Eng.  Rec.,  v.  62,  p.  444, 
Oct.  15,  1910;  Eng.  Rec.,  v.  64,  p.  199,  Aug.  12,  1911;  Eng.  Rec.,  v.  66, 
p.  596,  Nov.  30,  1912;  Eng.  News,  v.  64,  p.  262,  Sept.  8,  1910.  New 
York  and  Brooklyn  Bridge.  Eng.  News,  v.  8,  p.  171,  April  30,  1881; 
Eng.  News,  v.  8,  p.  181,  May  7,  1881;  Eng.  News,  v.  8,  p.  191,  May  14, 
1881;  Eng.  News,  v.  8,  p.  201,  May  21,  1881;  Eng.  News,  v.  8,  p.  212, 
May  28,  1881;  Eng.  News,  v.  8,  p.  223,  June  4,  i£8i;  Eng.  News,  v.  8,  p. 
232,  June  n,  1881;  Eng.  News,  v.  8,  p.  262,  July  2,  1881;  Eng.  News,  v. 
8,  P-  273,  July  9,  1881;  Eng.  News,  v.  8,  p.  283,  July  16,  1881;  Eng.  News, 
v.  8,  p.  291,  July  23,  1881;  Eng.  News,  v.  8,  p.  301,  July  30,  1881;  Eng. 
News,  v.  8,  p.  313,  Aug.  6,  1881.  Havre  de  Grace  Bridge.  Eng.  News, 
v.  12,  p.  245,  Nov.  22,  1884;  Eng.  News,  v.  13,  p.  14,  Jan.  3,  1885;  Eng. 
News,  v.  13,  p.  41,  Jan.  17,  1885;  Eng.  News,  v.  13,  p.  122,  Feb.  21,  1885; 
Eng.  News,  v.  13,  p.  228,  Apr.  n,  1885;  Eng.  News,  v.  13,  p.  244,  Apr.  18, 
1885;  Eng.  News,  v.  13,  p.  262,  Apr.  25,  1885;  Eng.  News,  v.  13,  p.  274, 
May  2,  1885.  Schuylkill  River  Bridge  of  the  B.  &  O.  R.  R.  Eng. 
News,  v.  15,  p.  85,  Feb.  6,  1886;  Eng.  News,  v.  15,  p.  195,  Mar.  27,  1886. 
Pivot  Pier  Caisson  for  a  Heavy  Swing  Bridge.  Eng.  News,  v.  51,  p.  5, 
Jan.  7,  1904.  New  Steel  Viaduct  between  Kansas  City,  Mo.  and 
Kansas  City,  Kans.  Eng.  News,  v.  58,  p.  323,  Sept.  26,  1907.  Pneu- 
matic Foundations  for  a  Bridge  across  the  Mississippi  River  at  Clinton, 
Iowa.  Eng.  News,  v.  61,  p.  67,  Jan.  21,  1909.  Pneumatic  Caissons  on 


584         REFERENCES   TO   ENGINEERING    LITERATURE      CHAP.  XIX 

the  B.  &  O.  R.  R.  Bridge  across  the  Susquehanna  River.  Eng.  News, 
v.  62,  546,  Nov.  18, 1909.  Caissons  of  the  McKinley  Bridge.  Eng.  News, 
v.  63,  p.  9,  Jan.  6,  1910.  Caissons  for  the  Sixth  Street  Viaduct,  Kansas 
City.  Trans.  Am.  Soc.  C.  E.,  v.  65,  p.  42,  Dec.,  1909.  Bridge  over  the 
Tennessee  River  at  Johnsonville,  Tenn.  Trans.  Am.  Soc.  C.  E.,  v.  33, 
p.  171,  March,  1895.  The  Substructure  of  the  Glasgow  Bridge  over  the 
Missouri  River.  Jour.  W.  Soc.  Engrs.,  v.  6,  p.  104,  Apr.,  1901.  Pneu- 
matic Foundations  of  the  Thebes  Bridge.  Trans.  Assoc.  C.  E.,  Cornell, 
1905,  p.  ii.  Construction  of  the  River  Piers  of  the  Pierre  Bridge. 
Eng.  Rec.,  v.  59,  p.  421,  Apr.  3,  1909. 

METAL  PNEUMATIC  CAISSONS. — Pneumatic  Caissons  of  the  Alexander 
III  Bridge.  Eng.  Rec.,  v.  37,  p.  275,  Feb.  26,  1898;  Eng.  News,  v.  39, 
p.  254,  Apr.  21,  1898;  Eng.  Mag.,  v.  14,  p.  515,  Dec.,  1897.  35  by  65- 
Foot  Steel  Caisson  Used  in  Wear  River  Bridge,  British  Isles.  Eng.  News, 
v.  62,  p.  9,  July  i,  1909.  Substructure  of  the  Seventh  Avenue  Swing 
Bridge.  Eng.  News,  v.  30,  p.  198,  Sept.  7,  1893;  R.  R.  Gaz.,  v.  24,  p. 
404,  June  3,  1892;  R.  R.  Gaz.,  v.  25,  p.  19,  Jan.  13,  1893;  Eng.  Rec., 
v.  28,  p.  38,  June  17,  1893. 

CYLINDER  PIER  CAISSONS. — Deep  Bridge  Foundations,  Atchafalaya 
River.  Eng.  Rec.,  v.  39,  p.  421,  Apr.  8,  1899;  Jour.  Assoc.  Eng.  Soc., 
v.  21,  p.  81,  Sept.  1898.  Pneumatic  Cylinder  Piers,  Valparaiso.  Eng. 
Rec.,  v.  38,  p.  556,  Nov.  26,  1898.  The  Merrimac  River  Bridge  at 
Newburyport,  Mass.  Eng.  Rec.,  v.  50,  p.  2j8,  Aug.  20,  1904.  Caissons 
for  a  Highway  Bridge  at  Trail,  British  Columbia.  Eng.  News,  v.  68, 
p.  1057,  Dec.  5,  1912. 

PHYSIOLOGICAL  EFFECTS  OF  COMPRESSED  AIR. — The  Caisson  Disease. 
Eng.  News,  v.  9,  p.  400,  Nov.  18,  1882.  Limit  of  Human  Endurance  of 
High  Air  Pressure.  Eng.  News,  v.  34,  p.  67,  Aug.  i,  1895.  Rules  for 
Working  in  Compressed  Air.  Eng.  News,  v.  40,  p.  405,  Dec.  22,  1898. 
Concerning  Caisson  Disease  and  Its  Prevention.  Eng.  News,  v.  41,  p. 
27,  Jan.  12,  1899.  A  igS-Foot  Dive  in  Tacoma  Harbor.  Eng.  News, 
v.  42,  p.  138,  Aug.  31,  1899.  The  Occurrence  and  Treatment  of  Caisson 
Disease.  Eng.  News,  v.  46,  p.  157,  Sept.  5,  1901;  Eng.  News,  v.  46,  p. 
167,  Sept.  5,  1901.  Some  Observations  on  the  Deep  Pneumatic  Work  of 
the  New  East  River  Bridge  Foundations.  Eng.  News,  v.  47,  p.  358, 
May  i,  1902.  How  to  Prevent  the  Bends.  Eng.  News,  v.  51,  p.  226, 
Mar.  10,  1904.  Caisson  Illness  and  Diver's  Palsy.  Eng.  News,  v.  51, 
p.  436,  May  5,  1904.  Caisson  Disease.  Eng.  News,  v.  51,  p.  60, 
Jan.  21,  1904.  Slow  Decompression  is  the  Best  Way  to  Prevent  the 
Bends.  Eng.  News,  v.  51,  p.  282,  Mar.  24,  1904.  Hospital  Air-Locks 
for  Caisson  Disease.  Eng.  News,  v.  51,  p.  178,  Feb.  25,  1904.  Disease 
of  Caisson  Workers.  Eng.  News,  v.  58,  p.  435,  Oct.  24,  1907.  Possi- 
bilities of  Working  at  Great  Depths  Under  Water.  Eng.  Rec.,  v.  33,  p. 
222,  Feb.  29,  1896.  Limits  of  Pneumatic  Caisson  Work.  Eng.  News,  v. 


ART.  200  PNEUMATIC    CAISSONS   FOR   BRIDGES  585 

36,  p.  112,  July  10,  1897.  Physiological  Effects  of  Compressed  Air. 
Eng.  News,  v.  47,  p.  125,  Jan.  31,  1903.  Caisson  Disease  and  a  Safety 
Apparatus  for  Pneumatic  Caisson  Locks.  Eng.  News,  v.  49,  p.  112, 
Jan.  23,  1904.  New  York  State  Law  Governing  Work  Under  Com- 
pressed Air.  Eng.  News,  v.  70,  p.  307,  Aug.  14,  1913.  Criticism  of 
New  York  Law  (In  not  providing  fresh  air  in  air-lock).  Eng.  News, 
v.  70,  p.  425,  Aug.  28,  1913.  French  and  Netherland  Requirements. 
Eng.  News,  v.  70,  p.  566,  Sept  18,  1913.  Investigation  of  the  Effect 
on  Man  of  High  Air  Pressure.  Eng.  Rec.,  v.  53,  p.  796,  June  30,  1906. 
The  Death  Roll  Due  to  Bends.  Eng.  Rec.,  v.  55,  p.  55,  Jan.  12,  1907. 
Caisson  Disease.  Eng.  Rec.,  v.  60,  p.  617,  Nov.  27,  1909.  Caisson 
Disease  and  Compressed  Air.  Eng.  Rec.,  v.  63,  p.  362,  Apr.  i,  1911. 
Compressed  Air  and  Its  Effects  on  Man.  Eng.  Rec.,  v.  63,  p.  347,  Apr. 
i,  1911.  Caisson  Disease  and  Its  Prevention.  Trans.  Am.  Soc.  C.  E., 
v.  65,  p.  i,  Dec.,  1909.  Cause,  Treatment  and  Prevention  of  the  Bends 
as  Observed  in  Caisson  Disease.  Jour.  Assoc.  of  Eng.  Soc.,  v.  39,  p. 
283,  Nov.,  1907.  Symposium  on  Caisson  Disease.  Eng.  News,  v.  68, 
p.  862,  Nov.  7,  1912.  Caisson  Disease  Experiences  and  Records. 
Compressed  Air,  1908.  Compressed  Air  Work  and  the  Hudson  Tunnels. 
Eng.  Mag.,  v.  n,  p.  937,  Aug.,  1896.  Health  of  Caisson  Workers. 
Eng.  Mag.,  v.  12,  p.  131,  Oct.,  1896.  Caisson  Disease.  Eng.  Digest, 
v.  3,  p.  381,  Apr.,  1908. 

ART.  200.    PNEUMATIC  CAISSONS  FOR  BUILDINGS 

GENERAL. — Foundations  of  the  Municipal  Building,  New  York  City. 
Eng.  News,  v.  63,  p.  24,  Jan.  6,  1910;  Eng.  News,  v.  64,  p.  523,  Nov.  17, 
1910;  Eng.  Rec.,  v.  62,  p.  522,  Nov.  5,  1910.  Substructure  of  the 
Guarantee  Trust  Building,  New  York.  Eng.  Rec.,  v.  65,  p.  44,  Apr.  20, 
1912.  Reinforced-concrete  and  steel-plate  caissons.  Steel  Substructure 
of  the  Woolworth  Building,  New  York  City.  Eng.  Rec.,  v.  65,  p.  177, 
Feb.  17,  1912;  Eng.  Rec.,  v.  64, 1256,  Aug.  26,  1911;  Eng.  Rec.,  v.  66,  p. 
97>  July  27>  1912.  Constructing  the  Foundations  of  the  Seaman's 
Church  Institute,  New  York.  Eng.  Rec.,  v.  65,  p.  105,  Jan.  27,  1912. 
Continuous  Caisson  Foundations  for  High  Buildings.  Eng.  Rec.,  v.  64, 
p.  318,  Sept.  16,  1911.  Large  Pneumatic  Foundations  of  the  New  York 
Telephone  Building.  Eng.  Rec.,  v.  65,  p.  610,  June  i,  1912.  New 
Foundations  for  the  Old  Boston  Custom  House.  Eng.  Rec.,  v.  63,  p. 
185,  Feb.  18,  1911.  Testing  Foundations  at  the  Municipal  Building, 
New  York.  Eng.  Rec.,  v.  63,  p.  196,  Feb.  18,  1911;  Eng.  Rec.,  v.  62,  p. 
46,  July  9,  1910;  Eng.  Rec.,  v.  62,  p.  57,  July  16,  1910.  Bryant  Building 
Substructure.  Eng.  Rec.,  v.  61,  p.  665,  May  21,  1910.  Metal  shell  and 
timber  caissons.  Development  of  Building  Foundations.  Eng.  Rec., 
v.  57,  p.  412,  Apr.  4,  1908.  Peculiar  Pneumatic  Caisson  Wreck.  Eng. 


586         REFERENCES    TO    ENGINEERING   LITERATURE       CHAP.  XIX 

Rec.,  v.  52,  p.  320,  Sept.  16,  1905.  Development  of  Architectural  Con- 
struction: Caisson  Foundations.  Eng.  News,  v.  38,  p.  190,  July  30, 
1898.  Recent  Developments  in  Pneumatic  Foundations  for  Buildings. 
Trans.  Am.  Soc.  C.  E.,  v.  61,  p.  211,  Dec.,  1908.  Pneumatic  Caisson 
Foundations  for  the  Adams  Express  Building.  Eng.  Rec.,  v.  66,  p.  320. 
Pneumatic  Caisson  Foundations  for  the  Adams  Express  Building.  Eng. 
Rec.,  v.  66,  p.  320,  Sept.  21,  1912. 

CAISSONS  OF  WOOD. — Pneumatic  Caisson  Foundations,  Emigrant 
Bank  Building.  Eng.  Rec.,  v.  63,  p.  568,  May,  20,  1911;  Eng.  Rec.,  v. 
60,  p.  528,  Nov.  6,  1909.  Substructure  of  the  Bankers  Trust  Company's 
Building.  Eng.  Rec.,  v.  62,  p.  677,  Dec.  10,  1910.  Pneumatic  Caisson 
Foundations,  Whitehall  Building,  New  York.  Eng.  Rec.,  v.  61,  p.  792, 
June  18,  1910.  Describes  tests  made  of  the  supporting  power  of  the  soil. 
Pneumatic  Foundations  of  the  City  Investing  Building,  New  York. 
Eng.  Rec.,  v.  55,  p.  267,  Mar.  2,  1907.  Trust  Company  of  America 
Building.  Eng.  Rec.,  v.  54,  p.  470,  Oct.  27,  1906.  Foundations  of  the 
Singer  Building  Extension.  Eng.  Rec.,  v.  55,  p.  116,  Feb.  2,  1907; 
Trans.  Am.  Soc.  C.  E.,  v.  63,  p.  i,  June,  1909.  Substructure  of  the 
United  States  Express  Company's  Building.  Eng.  Rec.,  v.  53,  p.  315, 
Mar.  3,  1906.  Constructing  Foundations  of  the  Trinity  Building,  New 
York.  Eng.  Rec.,  v.  50,  p.  283,  Sept.  3,  1904.  Caisson  Foundations 
for  a  Large  Steel  Cage  Office  Building  on  Broadway,  New  York.  Eng. 
Rec.,  v.  49,  p.  284,  Mar.  5,  1904.  Foundations  of  the  Rogers  Building, 
New  York.  Eng.  Rec.,  v.  49,  p.  362,  Mar.  19,  1904.  Auxiliary  Pneu- 
matic Caisson  Work  for  the  Bank  of  the  State  of  New  York.  Eng.  Rec., 
v.  48,  p.  245,  Aug.  29,  1903;  Eng.  Rec.,  v.  46,  p.  242,  Sept.  13,  1902. 
Foundations  of  the  Gillender  Building.  Eng.  Rec.,  v.  35,  p.  140,  Jan.  16, 
1897;  Eng.  News,  v.  37,  p.  13,  Jan.  7,  1897. 

CAISSONS  OF  WOOD  AND  STEEL. — Pneumatic  Caisson  Dam  Foundations, 
United  Fire  Companies  Building.  Eng.  Rec.,  v.  64,  p.  334,  Sept.  16, 
1911.  Blair  Building,  New  York.  Eng.  Rec.,  v.  46,  p.  227,  Sept.  6, 
1902.  Construction  of  the  Hanover  Bank  Building,  New  York.  Eng. 
Rec.,  v.  45,  p.  340,  Apr.  12,  1902.  Pneumatic  Caisson  Foundations  for 
the  New  York  Stock  Exchange  Building.  Eng.  Rec.,  v.  44,  p.  289, 
Sept.  28,  IQCI;  Eng.  News,  v.  46,  p.  222,  Sept.  26,  1901;  R.  R.  Gaz.,  v.  33, 
p.  662,  Sept.  27,  1901.  Foundations  of  the  Atlantic  Mutual  Insurance 
Company's  Building.  Eng.  Rec.,  v.  42,  p.  157,  Aug.  18,  1900.  Rapid 
Pneumatic  Foundation  Work.  Eng.  Rec.,  v.  40,  p.  509,  Oct.  28,  1899. 
Pneumatic  Caisson  Foundations  Under  a  Residence.  Eng.  Rec.,  v.  39, 
p.  31,  Dec.  10, 1898.  Pneumatic  Caisson  Foundations  for  Mrs.  Shepard's 
Residence.  Eng.  News,  v.  40,  p.  363,  Dec.,  8,  1898.  Good  description 
of  air-lock. 

CAISSONS  WITH  METAL  SHELLS. — Substructure  Work  of  the  Mutual 
Life  Building.  Eng.  Rec.,  v.  45,  p.  396,  Apr.  26,  1902.  Foundations 


ART.  201  PIER   FOUNDATIONS    IN    OPEN   WELLS  587 

of  the  Alliance  Building.  Eng.  Rec.,  v.  42,  p.  272,  Sept.  22,  1900.  Pneu- 
matic Caissons  of  the  Standard  Block.  Eng.  Rec.,  v.  38,  p.  108,  July  n, 
1896.  Foundations  of  the  Commercial  Cable  Building.  Eng.  Rec., 
v.  35,  p.  427,  Apr.  17,  1897;  R.  R.  Gaz.,  v.  28,  p.  390,  June  5, 
1896.  Foundations  of  the  Broad  Exchange  Building.  Eng.  News, 
v.  44,  p.  340,  Nov.  15,  1900.  Pneumatic  Foundations  for  the  Man- 
hattan Life  Building,  New  York.  Eng.  News,  v.  30,  p.  458,  Dec.  7, 
1893;  R.  R.  Gaz.,  v.  25,  p.  206,  Mar.  17,  1893;  R.  R.  Gaz.,  v.  25,  p.  882, 
Dec.  8,  1893.  Pneumatic  Caissons  of  the  American  Surety  Companies' 
Building.  Eng.  News,  v.  32,  p.  71,  July  26,  1894;  Eng.  Rec.,  v.  30,  p. 
104,  July  14,  1894. 

ART.  201.     PIER  FOUNDATIONS  IN  OPEN  WELLS 

OPEN  WELLS  WITH  SHEET-PILING. — Construction  of  the  New  Plaza 
Hotel,  New  York  City.  Eng.  Rec.,  v.  54,  p.  553,  Nov.  17,  1906.  Diffi- 
cult Foundations  of  the  Hoffman  House  Extension.  Eng.  Rec.,  v.  55, 
p.  296,  Mar.  2,  1907.  Deep  Open  Excavation  in  Quicksand.  Eng. 
Rec.,  v.  64,  p.  769,  Dec.  30,  1911.  Excavating  Caissons  Hydraulically 
at  St.  Louis.  Eng.  Rec.,  v.  66,  p.  262,  Sept.  7,  1912.  Foundations  of 
the  Bamberger  Building.  Eng.  Rec.,  v.  64,  p.  456,  Oct.  14,  1911. 
Foundations  of  the  Kinney  Building,  Newark,  N.  J.  Eng.  Rec.,  v.  66, 
p.  445,  Oct.  19,  1912.  Deep  Open  Pits  for  Foundation  Piers.  Eng.  Rec., 
v.  67,  p.  158,  Feb.  8,  1913.  Deep  Foundation  Pits  in  Quicksand.  Eng. 
Rec.,  v.  67,  p.  469,  Apr.  26,  1913. 

OPEN  WELLS  WITH  SHEETING. — Foundations  for  the  City  Hall  at 
Kansas  City.  Eng.  Rec.,  v.  25,  p.  292,  329,  403,  April  2,  16,  May  14, 
1892.  Chicago  Foundations.  Eng.  Rec.,  v.  52,  p.  131,  July  29,  1905. 
Development  of  Deep  Building  Foundations,  Chicago.  Eng.  News,  v. 
52,  p.  560,  Dec.  22,  1904.  Foundation  Work  on  the  Cook  County  Build- 
ing, Chicago.  Eng.  Rec.,  v.  53,  p.  800,  June  30,  1906.  Steel-Piling 
Foundations.  Eng.  Rec.,  v.  53,  p.  246,  Mar.  3,  1906.  Extension  Ribs 
and  Jacks  for  Caissons  and  Trenches.  Eng.  News,  v.  56,  p.  117,  Aug.  2, 
1906.  Foundations  of  the  Northwestern  Railway  Terminal,  Chicago. 
Eng.  Rec.,  v.  59,  p.  595,  May  8,  1909.  Foundations  for  the  New  City 
Hall  in  Chicago.  Eng.  Rec.,  v.  59,  p.  745,  June  12,  1909.  Piers  for 
Drawbridge  over  the  Calumet  River.  Eng.  Rec.,  v.  67,  p.  208,  Feb.  22, 
1913.  Chicago  Foundations.  Technograph,  No.  19,  p.  5,  1904-05. 
Foundations  in  Chicago.  Journal  Western  Soc.  of  Engrs.,  v.  10,  p.  687, 
1905.  Multiple-Spool  Hoist  for  Foundation  Work.  Eng.  News,  v. 
65>  P-  *33>  Feb.  2,  1911. 

GROUTING  PROCESS. — Cofferdam  without  Timber  or  Iron.  Eng.  News, 
v.  25,  p.  249,  Mar.  14,  1891;  Trans.  Am.  Soc.  C.  E.,  v.  24,  p.  234,  Mar., 
1891.  New  Process  for  Dealing  with  Quicksand.  Eng.  News,  v.  27, 


588         REFERENCES    TO    ENGINEERING   LITERATURE       CHAP.  XIX 

p.  420,  Apr.  28,  1892.  Making  Concrete  Foundations  in  Quicksand. 
Eng.  News,  v.  31,  p.  533,  June  28,  1894.  Grouting  the  Foundations  of 
the  Merrimac  River  Bridge.  Eng.  Rec.,  v.  50,  p.  218,  Aug.  20,  1904. 
Grouting  Foundations  for  a  Bridge  over  the  Danube  River  at  Ehingen. 
Eng.  News,  v.  47,  p.  35,  Jan.  9,  1902.  Grouting  Concrete  Viaduct 
Piers  at  Riverside,  Cal.  Eng.  Rec.,  v.  52,  p.  284,  Sept.  9,  1905.  Im- 
proved Methods  of  Constructing  Foundations  under  Water.  Trans. 
Am.  Soc.  C.  E.,  v.  29,  p.  639,  1893;  Trans.  Am.  Soc.  C.  E.,  v.  30,  p.  579, 
Dec.,  1893.  Tests  of  Grouting  Gravel  in  River  Beds.  Eng.  News, 
v.  69,  p.  979,  May  8,  1913. 

FREEZING  PROCESS.  —  Shaft  Sinking  by  Freezing—  Poetsch  Method. 
Eng.  News,  v.  n,  p.  282,  June  7,  1884;  Eng.  News,  v.  12,  p.  4,  July  5, 
1884;  Eng.  News,  v.  18,  p.  273,  Oct.  15,  1887;  Eng.  News,  v.  21,  p.  94, 
Feb.  2,  1889;  Eng.  News,  v.  21,  p.  601,  June  29,  1889;  Eng.  News,  v.  22, 
p.  103,  Aug.  3,  1889.  Freezing  Method  for  Subaqueous  Work.  Eng. 
Rec.,  v.  49,  p.  237,  Feb.  27,  1904.  Freezing  as  an  Aid  to  Excavation 
in  Unstable  Material.  Trans.  Am.  Soc.  C.  E.,  v.  52,  p.  365,  June,  1904. 
Sinking  a  Shaft  by  the  Freezing  Process  in  Germany.  Eng.  News,  v.  47, 
p.  340,  Apr.  24,  1902.  Sinking  a  Shaft  in  Quicksand  by  the  Freezing 
Process.  Eng.  News,  v.  50,  p.  65,  July  16,  1903.  Building  Foundation 
Constructed  by  the  Freezing  Process.  Eng.  News,  v.  69,  p.  214,  Jan.  30, 


ART.  202.    BRIDGE  PIERS 

GENERAL.  —  Dimensions  of  Masonry  Piers.  Street  Railway  Journal, 
v.  28,  p.  398,  Sept.  15,  1906.  Concrete  Piers.  Ry.  Age  Gaz.,  v.  46,  p. 
165,  Jan.  22,  1909.  Classified  cost.  Design  and  Construction  of  High 
Bridge  Piers.  Eng.  News,  v.  53,  p.  548,  May  25,  1905.  Valuable  article 
showing  method  of  design,  also  shows  examples  of  solid  piers  and  hollow 
pivot  piers.  Mingo  Bridge  Approaches.  Eng.  Rec.,  v.  49,  p.  789,  June 
25,  1904;  Eng.  Rec.,  v.  50,  p.  27,  July  2,  1904.  Gives  excellent  description 
of  methods  of  construction,  building  forms,  etc.  Concrete  Bridge  Piers. 
Eng.  News,  v.  30,  p.  296,  Oct.  12,  1893.  Early  use  of  all-concrete  piers. 
Stability  of  Stone  Structures.  Trans.  Am.  Soc.  C.  E.,  v.  8,  p.  238,  Sept., 
1879.  Concrete  Piers.  Trans.  Am.  Soc.  C.  E.,  v.  29,  p.  622,  Sept., 
1893;  Trans.  Am.  Soc.  C.  E.,  v.  30,  p.  567,  Dec.  1893.  Substructure  of 
Piscataquis  Bridge  and  Analysis  of  Concrete  Work.  Trans.  Am.  Soc. 
C.  E.,  v.  61,  p.  377,  Dec.,  1908.  Distribution  of  Pressure  on  Piers. 
Eng.  Mag.,  v.  12,  p.  869,  Feb.,  1897.  Design  of  Bridge  Foundations. 
Eng.  Rec.,  v.  38,  p.  376,  Oct.  i,  1898.  Bridge  Construction.  Trans. 
Assoc.  of  Civil  Engrs.,  Cornell  University,  v.  i,  p.  5,  Apr.,  1893.  Bridge 
Work  on  the  Kansas  City,  Pittsburgh  and  Gulf  Ry.  Eng.  News,  v.  40, 
p.  114,  Aug.  25,  1898.  Construction  of  Substructures  and  Foundations 


ART.  202  BRIDGE   PIERS  589 

within  a  Radius  of  Sixty  Miles  of  Pittsburgh,  by  E.  K.  Morse.     Proc. 
Engrs.  Soc.,  W.  Pa.,  v.  27,  p.  i,  Feb.,  1911. 

SOLID  PIERS. — Saybrook  Bridge  on  the  Connecticut  River.  Eng.  Rec., 
v.  65,  p.  186,  Feb.  17,  1912.  Stone  masonry  piers  on  pile  and  timber 
grillage  foundations.  Substructure  of  a  Double-Track  Railroad  Bridge 
at  Peoria,  111.  Eng.  Rec.,  v.  62,  p.  105,  July  23,  1910.  Reinforced  with 
rods.  Copper  River  Bridge  Piers.  Eng.  Rec.,  v.  61,  p.  642,  May  14, 
1910.  Starling  heavily  reinforced  with  old  rails.  Piers  of  the  Miles 
Glacier  Bridge.  Eng.  Rec.,  v.  61,  p.  559,  Apr.  23,  1910.  Heavily  rein- 
forced with  rails  against  ice  pressure.  Bridge  Piers  on  the  Guelph  and 
Goderich  Railway.  Eng.  Rec.,  v.  57,  p.  77,  Jan.  18,  1908.  Piers  of  the 
Columbia  River  Bridge.  Eng.  News,  v.  66,  p.  391,  Oct.  5,  1911.  Piers 
of  the  Cantilever  Bridge  over  the  Ohio  River  at  Beaver,  Pa.,  Pittsburgh 
and  Lake  Erie  R.  R.  Eng.  News,  v.  63,  p.  509,  May  5,  1910;  Proc.  Engrs. 
Soc.,  W.  Pa.,  v.  26,  p.  i,  Feb.,  1910.  Piers  of  the  McKinley  Bridge  across 
the  Mississippi  River  at  St.  Louis,  Mo.  Eng.  News,  v.  63,  p.  9,  Jan.  6, 

1910.  Large  Concrete  Pier.     Eng.  News,  v.  53,  p.  330,  Mar.  30,  1905. 
The  Mississippi  River  Cantilever  Bridge  at  Thebes,  111.     Eng.  News,  v. 
53,  p.  479,  May  n,  1905;  Eng.  Rec.,  v.  51,  p.  263,  Mar.  4,  1905.       New 
Westminster  Bridge  over   the  Fraser  River,  British   Columbia.     Eng. 
News,  v.  53,  p.  611,  June  15,  1905;  Eng.  Rec.,  v.  49,  p.  679,  May  28,  1904. 
High  Concrete  Piers  for  Railway  Bridge  across  Stone's  River;  Tennessee 
Central  Railway.     Eng.  News,  v.  47,  p.  251,  May  27, 1902.       Cumberland 
Extension  of  the  Western  Maryland  R.  R.     Eng.   News,  v.  51,  p.  304. 
Mar.  n,  1905.       Reinforced-Concrete  Piers  of  the  GilbertsviJle  Bridge. 
Eng.  Rec.,  v.  51,  p.  265,  Mar.  4,  1905;  R.  A.  Gaz.,  v.  39,  p.  31,  July  14, 
1905;  Eng.  News,  v.  53,  p.  548,  May  25,  1905.       Masonry  Construction 
for  the  Black  well's  Island  Bridge.     Eng.  Rec.,  v.  49,  p.  307,  Mar.  5,  1904; 
R.  R.  Gaz.,  v.  36,  p.  319,  Apr.  29,  1904.       Piers  for  a  Bridge  over  the 
Cuivre  River,  Burlington  &  Quincy  Railway.     Eng.  Rec.,  v.  49,  p.  557, 
Apr.  30,  1904.       Concrete  Piers  for  the  Red  River  Bridge,  St.  Louis  & 
San  Francisco  R.  R.     Eng.  News,  v.  19,  p.  443,  June  2,  1888.      Sub- 
structure of  the  Cairo  Bridge.     Eng.  News,  v.  25,  p.  122,  Feb.  7,  1891; 
Morison's,  "The  Cairo  Bridge."       New  Cornwall  Bridge  Piers.     Eng. 
Rec.,  v.  40,  p.  643,  Dec.  9,  1899. 

HOLLOW  PIERS.— Tall  Reinforced-Concrete  Bridge  Pier.  Eng.  Rec., 
v.  62,  p.  160,  Aug.  6,  1910.  St.  Louis  Municipal  Bridge  Substructure. 
Eng.  Rec.,  v.  62,  p.  427,  Oct.  15,  1910;  Eng.  News,  v.  65,  p.  320,  Mar.  16, 

1911.  Hollow  Concrete  Piers  on  the  Louisville  &  Nashville  R.  R.     Ry. 
Age  Gaz.,  v.  55,  p.  146,  July  25,  1913.       Design  of  the  Broadway  or 
Sparkman  Street  Bridge,  Nashville,  Tenn.     Eng.  News,  v.  62,'  p.  570, 
Nov.  25,  1909;  Eng.  News,  v.  61,  p.  199,  Feb.  25,  1909.       Substructure 
of  the  Mingo  Bridge.     Eng.  Rec.,  v.  48,  p.  393,  Oct.  3,  1903.       Monon- 
gahela  Bridge  Piers.     Eng.  Rec.,  v.  47,  p.  2,  Jan.  3,  1903.      The  Gunpow- 


5QO         REFERENCES   TO   ENGINEERING   LITERATURE       CHAP.  XIX 

der  and  Bush  River  Bridges.  Eng.  News,  v.  68,  p.  144,  Aug.  9,  1913; 
Eng.  &  Con.,  v.  41,  p.  195,  Feb.  n,  1914. 

VIADUCT  PIERS. — Construction  of  the  Substructure  of  the  Mulberry 
Street  Viaduct,  Harrisburg,  Pa.  Eng.  Rec.,  v.  58,  p.  228,  Aug.  29,  1908. 
Viaduct  Substructure,  Knoxville,  Cumberland  Gap  &  Louisville  R.  R. 
Trans.  Am.  Soc.  C.  E.,  v.  34,  p.  247,  Sept.,  1895;  Eng.  News,  v.  33,  p.  383, 
July  13,  1895.  Viaduct  Foundations.  Eng.  News,  v.  44,  p.  379,  Nov. 
29,  1900.  Piers  of  the  Soulevre  Viaduct,  France.  Eng.  News,  v.  23, 
p.  606,  June  28,  1890.  Viaduct  in  Portland  Cement  Concrete.  Eng. 
News,  v.  30,  p.  79.  Jan.  27,  1893.  Difficult  Pier  Construction,  Man- 
hasset  Viaduct,  Long  Island  Railway.  Eng.  News,  v.  41,  p.  18,  Jan.  12, 
1899.  Bridgeport  Improvements  of  the  New  York,  New  Haven  & 
Hartford  Railway.  Eng.  Rec.,  v.  50,  p.  104,  July  23,  1904;  Eng.  Rec., 
v.  50,  p.  127,  July  30,  1904.  Cost  of  Small  Concrete  Piers  for  Viaduct 
Supports.  Eng.  Rec.,  v.  59,  p.  no,  Jan.  23,  1909.  Cost  of  Piers  of  the 
Chattahoochee  River  Viaduct.  Eng.  Rec.,  v.  58,  p.  233,  Aug.  29,  1908. 

METAL  SHELL  CYLINDER  PIERS. — Cylinder-Pier  Bridges,  C.  &  N.  W. 
Ry.  Eng.  News,  v.  68,  p.  748,  Oct.  24,  1912.  Cylinder  Piers  of  the 
Norfolk  &  Western  Bridge  No.  5,  Elizabeth  leaver,  Norfolk,  Va.  Eng. 
News,  v.  61,  p.  620,  June  10,  1909.  Modern  Highway  Bridge  Construc- 
tion. Eng.  News,  v.  64,  p.  209,  Aug.  25,  1910.  Substructure  of  the 
Dumbarton  Point  Bridge.  Eng.  Rec.,  v.  62,  p.  172,  Aug.  13,  1910; 
Trans.  Am.  Soc.  C.  E.,  v.  76,  p.  1572,  Dec.,  1913.  Tensas  River  Bridge. 
Eng.  News,  v.  13,  p.  386,  June  20,  1885.  Bridge  Foundations  in  Nova 
Scotia.  Trans.  Am.  Soc.  C.  E.,  v.  29,  p.  622,  Sept.,  1893;  Trans.  Am.  Soc. 
C.  E.,  v.  30,  p.  567,  Dec.,  1893.  Design  of  Concrete  Piers  with  Metal 
Shells.  Eng.  News,  v.  48,  p.  379,  Nov.  6,  1902.  Cylinder  Piers  of  the 
New  Portland  Bridge.  Eng.  Rec.,  v.  53,  p.  252,  Mar.  3,  1906.  Steel 
Wharves  at  Manila.  Eng.  Rec.,  v.  53,  p.  741,  June  16,  1906.  Dunsbach 
Ferry  Bridge.  Eng.  News,  v.  44,  p.  54,  July  20,  1901.  Greenfield 
Street  Railway  Bridge,  Greenfield,  Mass.  Eng.  Rec.,  v.  49,  p.  462,  Apr. 
9,  1904. 

REINFORCED- CONCRETE  CYLINDER  PIERS. — Piers  for  Bridge  over  the 
St.  Croix  River  at  Hudson,  Wis.  Eng.  Rec.,  v.  69,  p.  192,  Feb.  14,  1914. 
Lift  Bridges  over  the  Buffalo  River.  Ry.  Age  Gaz.,  v.  54,  p.  197,  Jan.  31, 
1913.  Reinforced-Concrete  Piers  for  a  Bridge  at  Stakeford,  England. 
Eng.  News,  v.  63,  p.  193,  Feb.  17,  1910. 

PIVOT  PIERS. — Substructure  of  the  East  Haddam  Bridge.  Eng.  Rec., 
v.  66,  p.  630,  Dec.  7,  1912.  Substructure  of  the  St.  Louis  River  Bridge. 
Eng.  Rec.,  v.  65,  p.  582,  May  25,  1912.  Pivot  Pier  of  the  Chelsea  Bridge 
North.  Eng.  News,  v.  68,  p.  138,  Aug.  2,  1913.  Pivot  Pier  of  the 
Gilbertsville  Bridge.  Eng.  Rec.,  v.  51,  p.  265,  Mar.  4,  1905;  Eng.  News, 
v-  53>  P-  548,  May  25,  1905.  Draw  Foundation  Pier  for  Charlestown 
Bridge.  Eng.  Rec.,  v.  38,  p.  186,  July  30,  1898.  Substructure  of  the 


ART.  203  BRIDGE    ABUTMENTS  591 

Dumbarton  Point  Bridge.  Eng.  Rec.,  v.  62,  p.  172,  Aug.  13,  1910; 
Trans.  Am.  Soc.  C.  E.,  v.  76,  p.  1572,  Dec.,  1913.  The  New  Portland 
Bridge.  Eng.  Rec.,  v.  53,  p.  252,  Mar.  3,  1906.  Pivot  Pier  of  the 
Interstate  Bridge,  Omaha,  Neb.  Eng.  News,  v.  30,  p.  410,  Nov.  23,  1893. 


ART.  203.    BRIDGE  ABUTMENTS 

GENERAL. — Design  of  High  Abutments.  Eng.  News,  v.  55,  p.  36, 
Jan.  ii,  1906.  Economical  Concrete  Abutment.  Eng.  News,  v.  55, 
p.  296,  Mar.  15,  1906.  Heaving  of  Bridge  Abutments  by  Frost  in  the 
Ground.  Eng.  News,  v.  59,  p.  260,  Mar.  5,  1908.  Designing  Concrete 
Abutments  for  Steel  Highway  Bridges.  Eng.  News,  v.  65,  p.  190,  Feb. 
16,  1911;  Eng.  Rec.,  v.  63,  p.  305,  Mar.  18,  1911.  Gives  diagrams  for 
estimating  the  amount  of  concrete  and  the  cost  of  abutments.  Abut- 
ments for  a  Reinforced-Concrete  Girder  Bridge  at  Stakeford,  England. 
Eng.  News,  v.  63,  p.  193,  Feb.  17,  1910.  Concrete  Pedestal  Bridge 
Abutments  on  the  New  York  State  Barge  Canal.  Eng.  News,  v.  64,  p. 
180,  Aug.  18,  1910;  Eng.  Rec.  v.  61,  p.  154,  Feb.  5,  1910.  Design  of 
Railway  Bridge  Abutments.  J.  H.  Prior,  Proc.  Am.  Ry.  Eng.  Assoc., 
1912,  v.  13,  p.  1086.  Discussion  of  Design  and  Specifications  for  a 
Reinforced-Concrete  Bridge  Abutment.  Trans.  Can.  Soc.  C.  E.,  v.  21, 
p.  173,  1907.  Abutments  for  the  Delaware  River  Bridge,  New  York, 
Ontario  and  Western  R.  R.,  Hancock,  New  York.  Eng.  News,  v.  66, 
p.  725,  Dec.  21,  1911.  Reinforced  arch  abutments. 

WING- WALL  ABUTMENTS. — Concrete  Abutment  and  Parapet  Wall  for 
a  Skew  Bridge,  Ulster  &  Delaware  Railroad.  Eng.  News,  v.  50,  p.  270, 
Sept.  24,  1903;  R.  R.  Gaz.,  v.  37,  p.  602,  Dec.  2,  1904.  Reinforced- 
Concrete  Abutment  for  a  Bridge  on  the  Lehigh  Valley  R.  R.,  at  Towanda, 
Pa.  Eng.  News,  v.  57,  p.  277,  Mar.  14,  1907.  Buttressed  type.  Novel 
Concrete-Steel  Bridge  Abutment  on  the  Wabash  R.  R.  Eng.  News,  v. 
52,  p.  62,  July  21,  1904.  Buttressed  type.  Abutments  on  the  Chicago, 
Milwaukee  &  St.  Paul  Ry.  Eng.  News,  v.  63,  p.  160,  Feb.  10,  1910. 
Reinforced-Concrete  Abutments  on  the  Atlantic,  Birmingham,  &  Atlantic 
R.  R.  Eng,  Rec.,  v.  56,  p.  100,  July  27,  1907;  Ry.  Age  Gaz.,  v.  45,  p.  23, 
July,  1908.  Substructure  of  a  Double-Track  Railroad  Bridge,  Peoria. 
Eng.  Rec.,  v.  62,  p.  105,  July  23,  1910.  Substructure  of  the  St.  Louis 
River  Bridge.  Eng.  Rec.,  v.  65,  p.  582,  May  25,  1912. 

U-ABUTMENTS  AND  T-ABUTMENTS. — Abutments  for  Long  Span  Rein- 
forced-Concrete Girder  Bridges  on  the  West  Perm.  R.  R.  Eng.  News, 
v.  63,  p.  87,  Jan,  27,  1910.  Abutments  on  the  Cumberland  Extension 
of  the  Western  Maryland  R.  R.  Eng.  Rec.,  v.  51,  p.  304,  Mar.  n,  1905. 
New  Type  of  U- Abutment.  Eng.  Rec.,  v.  61,  p.  100,  Jan.  22,  1910. 
Method  of  Figuring  Foundation  Pressures  under  U-Abutments.  Eng. 


5Q2         REFERENCES    TO    ENGINEERING   LITERATURE      CHAP.  XIX 

Rec.,  v.   62,  p.   560,  Nov.   19,   1910.       Concrete  Bridge  Abutment  of 
T-Section.     Eng.  News,  v.  57,  p.  187,  Feb.  14,  1907. 

BURIED  ABUTMENTS. — Abutments  of  the  Beaver  Bridge.  Eng.  News, 
v.  63,  p.  510,  May  5,  1910.  Abutment,  for  the  East  Haddam  Bridge. 
Eng.  Rec.,  v.  66,  p.  630,  Dec.  7,  1912.  Design  of  Concrete  Abut- 
ments Without  Wing  Walls  for  Deck  Girders.  Eng.  News,  v.  70, 
p.  816,  Oct.  23,  1913.  Abutments  of  the  Mingo  Bridge.  Eng.  Rec., 
v.  49,  p.  789,  June  25,  1904.  Haw  Creek  Bridge  Abutment.  Eng.  Rec., 
v.  50,  p.  476,  Oct.  22,  1904. 

ART.  204.     SPREAD  FOUNDATIONS 

GENERAL. — Sand  Foundations  for  High  Buildings.  Eng.  Rec.,  v.  66, 
p.  310,  Sept.  21,  1912.  Development  of  Building  Foundations.  Eng. 
Rec.,  v.  57,  p.  412,  Apr.  4,  1908.  Tall  Building  Foundation  on  Soft 
Clay.  Eng.  Rec.,  v.  55,  p.  731,  June  22,  1907.  Gives  results  of  tests. 
Reinforced-concrete  footings  adopted.  Permissible  Reduction  of  Live 
Loads  under  Footings  of  Buildings  More  Than  Three  Stories  High. 
Schneider's  "General  Specifications  for  Structural  Work  of  Buildings," 
p.  58,  1910.  Chicago  Foundations.  P.  C.  Shankland.  Eng.  Rec., 
v.  52,  p.  131,  July  29,  1905.  Proportioning  of  Foundations  for  Columns 
and  Walls.  Eng.  News,  v.  69,  p.  465,  Mar.  6,  1913. 

STEEL  I-BEAM  GRILLAGE  FOUNDATIONS. — General  Features  of  the 
Curtis  Building,  Phila.  Eng.  Rec.,  v.  62,  p.  41,  July  9,  1910.  Phelan 
Building,  San  Francisco.  Eng.  Rec.,  v.  57,  p.  366,  Mar.  28,  1908.  Dis- 
tributing Column  Loads  on  Irregular  Grillage  Foundations.  Eng.  Rec., 
v.  64,  p.  632,  Nov.  25,  1911.  Curtis  Power  Building.  Eng.  Rec.,  v.  63, 
p.  17,  Jan.  7,  1911.  Design  of  I-beam  Grillages  for  Foundations.  See 
"Cambria  Steel,"  by  Cambria  Steel  Company,  also  "Pocket  Companion," 
by  Carnegie  Steel  Company.  Steel  Foundations  of  the  Title  Guarantee 
and  Trust  Company  Building,  New  York  City.  Eng.  Rec.,  v.  53,  p.  531, 
April  28,  1906.  Foundation  Details,  New  Office  Building,  New  York 
Central  Lines.  Eng.  Rec.,  v.  53,  p.  224,  Feb.  24,  1906.  Steel  Beam 
Grillage  Foundations.  Eng.  Rec.,  v.  38,  p.  99,  July  2,  1898.  Rein- 
forced Wall  Foundations  on  Yielding  Subsoil.  Eng.  News,  v.  60,  p.  5, 
July  2,  1908. 

REINFORCED-CONCRETE  SPREAD  FOUNDATIONS. — Novel  Type  of  Canti- 
lever Foundation.  Eng.  News,  v.  68,  p.  995,  Nov.  28,  1912.  Slab  and 
Box  Foundation  for  Chimneys  and  Columns.  Eng.  Rec.,  v.  65,  p.  636, 
June  8,  1912.  Inverted- Arch  Foundation  of  Reinforced  Concrete. 
Eng.  News,  v.  66,  p.  763,  Dec.  28,  1911.  Reinforced-Concrete  Raft 
Foundations  for  Tall  Buildings.  Eng.  Rec.,  v.  64,  p.  622,  Nov.  25,  1911. 
Foundations  of  the  Logan  Building  at  Youngstown.  Eng.  Rec.,  v.  58, 
p.  278,  Sept.  5,  1908.  Reinforced-Concrete  Work  at  the  New  Railway 


ART.  205  UNDERPINNING  BUILDINGS  593 

Terminal  Station  at  Atlanta,  Ga.  Eng.  Rec.,  v.  55,  p.  399,  Apr.  12,  1906. 
Spread  Foundation  of  Reinforced  Concrete  for  a  Six-Story  Building. 
Eng.  News,  v.  54,  p.  77,  July  20,  1905.  Reinforced-Concrete  Candy 
Factory.  Eng.  Rec.,  v.  64,  p.  506,  Oct.  28,  1911.  Long  Foundation 
Girders  for  a  Loft  Building.  Eng.  Rec.,  v.  64,  p.  580,  Nov.  IT,  1911. 
Reinforced-Concrete  Footings  for  the  Factories  for  the  Bush  Terminal. 
Eng.  Rec.,  v.  53,  p.  36,  Jan.  13,  1906.  Substructure  of  the  New  Meier  & 
Frank  Building.  Eng.  Rec.,  v.  60,  p.  148,  Aug.  7,  1909.  Cantilever  and 
Raft  Foundation  for  a  Twelve-Story  Building.  Eng.  Rec.,  v.  59,  p.  362, 
Mar.  27,  1909.  Method  of  Enlarging  Column  Footings.  Eng.  Rec.,  v. 
58,  p.  487,  Oct.  31,  1908.  The  Substructure  of  the  Pope  Building, 
Cleveland,  Ohio.  Eng.  Rec.,  v.  58,  p.  354,  Sept.  26,  1908;  Eng.  Rec., 
v.  58,  p.  489,  Oct.  31,  1908.  Beam  grillages  with  reinforced-concrete 
spread  footing.  Reinforced-Concrete  Store  Building  in  Chicago.  Eng. 
Rec.,  v.  49,  p.  7 13,  June  4,  1904.  Design  of  Reinforced-Concrete  Footing 
"Concrete,  Plain  and  Reinforced,"  by  Taylor  and  Thompson. 

ART.  205.    UNDERPINNING  BUILDINGS 

GENERAL. — Underpinning  the  Cambridge  Building;  New  York  City. 
Trans.  Am.  Soc.  C.  E.,  v.  67,  p.  553,  June,  1910.  Underpinning  Buildings 
near  Excavations,  New  York  City.  Eng.  Rec.,  v.  60,  p.  598,  Nov.  27, 
1909.  Underpinning  a  Leaning  Chimney.  Eng.  Rec.,  v.  60,  p.  27, 
July  3, 1909;  Eng.  News,  v.  62, p .  n,  July  i,  1909.  Shoring  and  Straight- 
ening a  Four-Story  Building  in  Milwaukee.  Eng.  Rec.,  v.  59,  p.  480, 
Apr.  TO,  1909.  Problem  in  Underpinning.  Eng.  Rec.,  v.  56,  p.  94, 
July  27,  1907.  Underpinning  a  7o-Foot  Wall  without  Temporary 
Supports.  Eng.  Rec.,  v.  52,  p.  90,  July  22,  1905.  Transferring  a  2000- 
Ton  Wall  to  Columns  and  Girders.  Eng.  Rec.,  v.  52,  p.  523,  Nov.  4,  1905. 
Underpinning:  Supporting  a  Brick  Wall  from  One  Side  Only.  Eng. 
Rec.,  v.  43,  p.  525,  June  i,  1901.  Underpinning  High  Masonry  Struc- 
tures. Eng.  Rec.,  v.  43,  p.  no,  Feb.  2,  1901.  Underpinning  without 
Supports.  Eng.  Rec.,  v.  40,  p.  415,  Sept.  30, 1899.  Retaining  Walls  and 
Underpinning.  Proc.  Am.  Soc.  C.  E.,  v.  28,  p.  202,  Mar.,  1902.  Under- 
pinning Buildings.  Eng.  Rec.,  v.  57,  p.  420,  Apr.  4,  1908. 

NEEDLE-BEAM  UNDERPINNING. — Underpinning  the  Cross  Building. 
Eng.  News,  v.  68,  p.  1134,  Dec.  19,  1912.  Shoring  and  Remodeling  the 
Front  of  a  New  York  Building.  Eng.  Rec.,  v.  65,  p.  296,  Mar.  16,  1912; 
Eng.  Rec.,  v.  65,  p.  392,  Apr.  6,  1912.  Deep  Underpinning  Through 
Sand.  Eng.  Rec.,  v.  62,  p.  461,  Oct.  22,  1910.  Underpinning  a  300-Ton 
Column  on  Quicksand.  Eng.  Rec.,  v.  61,  p.  649,  May  14, 1910.  Knicker- 
bocker Trust  Building  Substructure.  Eng.  Rec.,  v.  59,  p.  537,  Apr.  24, 
1909.  Underpinning  Buildings  Adjacent  to  The  Bridge  Loop  Subway, 
New  York.  Eng.  Rec.,  v.  57,  p.  263,  Mar  7,  1908.  Underpinning 
38 


594         REFERENCES   TO    ENGINEERING   LITERATURE      CHAP.  XIX 

Six-Story  Apartment  Houses  in  New  York  City.  Eng.  Rec.,  v.  57,  p.  689, 
Miay  30,  1908.  Underpinning  Adjacent  to  the  Silversmiths'  Building, 
New  York  City.  Eng.  Rec.,  v.  56,  p.  346,  Sept  28,  1907.  Combined 
Underpinning  and  Sheeting  Job.  Eng.  Rec.,  v.  56,  p.  254,  Sept.  7,  1907. 
Underpinning  Job  on  the  Washington  Street  Subway,  Boston.  Eng. 
Rec.,  v.  55,  p.  266,  May  2,  1907.  Underpinning  Foundations  Adjacent 
to  the  City  Investing  Building,  New  York.  Eng.  Rec.,  v.  55,  p.  267. 
Mar.  2,  1907.  Cantilever  Underpinning  in  Boston.  Eng.  Rec.,  v.  55, 
p.  700,  June  15,  1907.  Methods  Used  in  Underpinning  the  Singer 
Building,  New  York.  Eng.  Rec.,  v.  55,  p.  275,  Mar.  2,  1907.  Under- 
pinning a  Tall  Brewery  Wall  on  Rock  Foundations.  Eng.  Rec.,  v.  54, 
p.  20,  July  7,  1906.  Underpinning  the  Marshall  Field  Building  in 
Chicago.  Eng.  Rec.,  v.  53,  p.  552,  May  5,  1906.  Underpinning  the 
Criterion  Hotel,  New  York.  Eng.  Rec.,  v.  53,  p.  692,  June  2,  1906. 
Foundations  of  the  Myers  Building,  Albany.  Eng.  Rec.,  v.  53,  p.  802, 
June  30,  1906.  Underpinning  the  Grand  Central  Palace,  New  York. 
Eng.  Rec.,  v.  53,  p.  798,  June  30,  1906.  '  Underpinning  Brooklyn 
Stores.  Eng.  Rec.,  v.  53,  p.  58,  Jan.  13,  1906.  Underpinning  Heavy 
Buildings.  Eng.  Rec.,  v.  53,  p.  782,  June  30,  1906.  Underpinning 
and  Protecting  the  Foundations  of  the  Times  Building,  New  York. 
Eng.  Rec.,  v.  51,  p.  595,  May  27,  1905.  Underpinning  the  Sears  Building, 
Boston.  Eng.  Rec.,  v.  51,  p.  351,  Mar.  25,  1905.  Underpinning  an  Old 
Office  Building  on  Broadway,  New  York.  Eng.  Rec.,  v.  48,  p.  698, 
Dec.  5,  1903.  Direct  and  Indirect  Supports  for  Underpinning  a  High 
Wall.  Eng.  Rec.,  v.  47,  p.  294,  Mar.  21,  1903.  Complicated  Under- 
pinning. Eng.  Rec.,  v.  46,  p.  299,  Sept.  27,  1902.  Underpinning 
Buildings  Adjacent  to  the  Adams  Express  Building,  New  York.  Eng. 
Rec.,  v.  66,  p.  320,  Sept.  21,  1912.  Lifting  and  Underpinning  a  Nine- 
Story  Wall.  Eng.  Rec.,  v.  45,  p.  373,  Apr.  19,  1902.  Construction  of 
the  East  Market  Street  Subway,  Phila.  Proc.  Engrs.  Club  of  Phila.,  v. 
25,  p.  219,  1908.  Underpinning  the  Decker  Building,  New  York. 
Eng.  Rec.,  v.  45,  p.  442,  May  10,  1902. 

BREUCHAUD  METHOD. — Deep  Underpinning  in  a  Very  Narrow  Clear- 
ance. Eng.  Rec.,  v.  64,  p.  276,  Sept.  2,  1911.  Underpinning  a  Fifteen- 
Story  Building  on  Grillage  Foundations.  Eng.  Rec.,  v.  64.  p,  307, 
Sept.  9,  1911.  Underpinning  Buildings  Adjacent  to  the  United  Fire 
Companies  Building.  Eng.  Rec.,  v.  64,  p.  334,  Sept.  16,  1911.  Under- 
pinning the  Astor  Building,  New  York.  Eng.  Rec.,  v.  62,  p.  17,  June  2, 
1910.  Underpinning  the  Mt.  Siani  Hospital  Dispensary.  Eng.  Rec., 
v.  61,  p.  478,  Apr.  2,  1910.  Underpinning  Buildings  Adjacent  to  the 
Farmers'  Loan  and  Trust  Company's  Building,  New  York.  Eng.  Rec., 
v.  58,  p.  480,  Oct.  31, 1908.  Trust  Company  of  America  Building.  Eng. 
Rec.,  v.  54,  p.  442,  Oct.  20,  1906.  Underpinning  Old  Walls  with  Steel 
Columns.  Eng.  Rec.,  v.  53,  433,  Mar.  31,  1906.  Substructure  Work  for 


ART.  206  EXPLORATIONS   AND   UNIT   LOADS  595 

The  Mutual  Life  Building,  New  York.  Eng.  Rec.,  v.  45,  p.  368,  Apr.  19, 
1902.  Underpinning  of  Heavy  Buildings.  Trans.  Am.  Soc.  C.  E.,  v.  37, 
p.  31,  June,  1897.  Underpinning  the  Stokes  Building,  New  York  City. 
Eng.  Rec.,  v.  34,  p.  183,  Aug.  8,  1896.  Underpinning  Heavy  Buildings. 
Eng.  Rec.,  v.  35,  p.  144,  Jan.  16,  1897.  Shoring  the  Walls  of  An  Old 
Building.  Eng.  Rec.,  v.  37,  p.  211,  Feb.  5,  1898.  New  Method  of 
Underpinning  Heavy  Buildings.  Eng.  News,  v.  37,  p.  6,  Jan.  7,  1897. 
Foundations  of  the  New  Mutual  Life  Building.  Eng.  News,  v.  45,  p.  221, 
Mar.  28,  1901. 

ART.  206.    EXPLORATIONS  AND  UNIT  LOADS 

BORINGS  WITH  AUGERS. — Test  Borings  for  Foundations.  Eng.  News,  v. 
21,  p.  324,  April  13,  1889.  Exploration  of  Soil  by  Wood  Augers.  Eng. 
News,  v.  41,  p.  175,  Mar.  16,  1899. 

WASH  BORINGS. — Sinking  Foundation  Test  Holes  with  a  Water-Jet. 
Eng.  Rec.,  v.  25,  p.  95,  Jan.  9,  1892.  Methods  and  Results  of  Surveys 
and  Borings  for  Oswego-Mohawk  Ship  Canal  Route  for  U.  S.  Board  of 
Engineers  on  Deep  Water-ways.  D.  J.  Howell.  Eng.  News,  v.  43,  p. 
418,  June  28,  1900.  Borings  for  the  Bohio  Dam  for  the  Panama  Canal. 
R.  C.  Smith.  Jour.  W.  Soc.  Engrs.,  v.  8,  p.  372,  Aug.,  1903.  Suggested 
method  of  Recording  Earth  Borings.  E.  R.  Shnable.  Eng.  News,  v. 
53>  P-  20,  Jan.,  5  1905.  Wash  Drill  Borings  on  the  New  York  State 
Barge  Canal.  EmileLow.  Eng.  News,  v.  57,  p.  54,  Jan.  17,  1907.  Cost 
of  Wash  Drill  Borings  on  the  Deep  Water-ways  Surveys,  1897  to  1900. 
Eng.  News,  v.  57,  p.  57,  Jan.  17,  1907.  Wash  Borings  for  the  Rapid 
Transit  Commission,  New  York  City.  Eng.  News,  v.  57,  p.  58,  Jan.  17, 
1907.  Cost  of  Boring  Five  Test  Wells  for  a  Double-Track  Railway 
Bridge  in  California.  P.  J.  Robinson.  Engr.-Contr.,  v.  33,  p.  9,  Jan.  5, 
1910.  Borings  for  the  Panama  R.  R.  Dock  at  Cristobal,  with  Table  of 
Costs.  E.  B.  Karnopp.  Eng.  News,  v.  63,  p.  691,  June  16,  1910.  Jack 
for  Pulling  Drill  Rods  and  Sounding  Bars.  Eng.  Rec.,  v.  67,  p.  37,  Jan.  n, 
1913.  Sub-surface  Investigations  on  the  Catskill  Aqueduct,  Board  of 
Water-supply.  Robert  Ridgway.  Eng.  Rec.,  v.  57,  p.  522,  April  18, 
1908. 

CORE  DRILLING  WITH  DIAMONDS. — Explorations  for  Hudson  River 
Crossing  of  the  Catskill  Aqueduct,  New  York  City.  Alfred  D.  Flinn. 
Eng.  News,  v.  59,  p.  358,  April  2,  1908.  Sub-surface  Investigation  on  the 
Catskill  Aqueduct,  Board  of  Water-supply.  Robert  Ridgway.  Eng. 
Rec.,  v.  57,  p.  557,  April  25,  1908.  Standard  Symbols  for  Borings.  Eng. 
Rec.,  v.  65,  p.  378,  April  6,  1912.  Diamond  Borings.  New  East  River 
Bridge  Foundations.  Eng.  News,  v.  36,  p.  198,  Sept.  24,  1896.  Ex- 
perience in  Diamond  Drill  Work  on  the  Deep  Water-ways  Survey,  with 
Statistics  of  Cost.  Eng.  News,  v.  50,  p.  83,  July  23,  1903.  Cost  of 


596         REFERENCES    TO    ENGINEERING   LITERATURE       CHAP.  XIX 

Diamond  Drilling.  Eng.  News,  v.  57,  p.  389,  April  4,  1907.  Testing 
Diamond  Drill  Borings  at  the  Site  of  the  Olive  Bridge  Dam,  Ashokan 
Reservoir.  Eng.  Rec.,  v.  58,  p.  25,  July  4,  1908.  Methods  and  Costs  of 
Testing  for  Bridge  Foundations.  F.  H.jBainbridge.  Engr.-Contr., 
v.  30,  p.  352,  Nov.  25,  1908.  New  Bridge  Crossing  of  the  Mississippi 
River  at  Clinton,  Iowa,  C.  &  N.  W.  Ry.  F.  H.  Bainbridge.  Eng.  News, 
v.  6 1,  p.  68,  Jan.  21,  1909.  Cost  of  Diamond  Drill  Work.  Eng.  Rec., 
v.  59,  p-  346,  Mar.  27,  1909.  Inclined  Diamond  Drill  Borings  under  the 
Hudson  River.  Eng.  Rec.,  v.  61,  p.  68,  Jan.  15,  1910.  Core  Drilling  un- 
der the  Hudson  River  for  the  Catskill  Aqueduct.  Wm.  E.  Swift.  Eng. 
News,  v.  63,  p.  414,  April  7,  1910.  Methods  of  Conducting  Test  Borings 
and  of  Sinking  Shafts  for  the  Hudson  River  Crossing  in  the  Catskill 
Aqueduct.  Engr.-Contr.,  v.  34,  p.  356,  Oct.  26,  1910.  Cost  of  Diamond 
Drilling  and  Depreciation  of  Diamonds.  Engr.-Contr.,  v.  37,  p.  462, 
April  24,  1912.  Time  lost  in  Diamond  Drilling  Operations.  Engr.- 
Contr.,  v.  39,  p.  93  Jan.  22,  1913. 

CORE  DRILLING  WITHOUT  DIAMONDS. — Davis  *  Calyx'  Core  Drill. 
Eng.  News,  v.  45,  p.  334,  May  9,  1901.  Methods  of  making  Test 
Borings  for  the  Catrkill  Reservoirs  for  the  New  York  Water-supply  with 
some  Plant  Costs.  Engr.-Contr.,  v.  31,  p.  511,  June  23,  1909.  Pre- 
cautions in  Interpreting  Records  of  Test  Borings.  Engr.-Contr.,  v.  33, 
p.  585,  June  29,  1910.  See  also  articles  in  preceding  paragraph  on  borings 
for  Catskill  Aqueduct,  Board  of  Water-supply,  New  York  City. 

TESTS  FOR  BEARING  CAPACITY. — Preliminary  Foundation  Tests  for  the 
St.  Paul  Building.  Eng.  Rec.,  v.  33,  p.  388,  May  2,  1896.  Safe  Load 
on  Soil  at  New  Orleans,  La.  Eng.  News,  v.  41,  p.  3303,  May  n,  1898  and 
correction  on  p.  333.  Foundation  Construction  for  the  New  York 
Capitol  for  South  Dakota.  Samuel  H.  Lea.  Eng.  Rec.,  v.  57,  p.  437, 
April  4,  1908.  Bearing  Tests  for  Heavy  Foundation  Loads.  Eng. 
Rec.,  v.  60,  p.  55,  July  10,  1909.  Testing  Bearing  Power  of  Hard-Pan. 
Extension  Whitehall  Building,  New  York  City.  Eng.  Rec.,  v.  61,  p.  792, 
June  18,  1910.  Tests  and  Costs  of  making  a  Test  of  the  Bearing  Power 
of  Soil  for  a  Building.  Engr.-Contr.,  v.  34,  p.  31,  July  13, 1910.  Tests  of 
Bearing  Capacity  of  Sand  under  Municipal  Building,  New  York  City. 
Eng.  Rec.,  v.  62,  p.  46,  July  9,  1910;  p.  57,  July  16,  1910;  Eng.  News, 
v.  63,  p.  24,  Jan.  6, 1910;  v.  64,  p.  525,  Nov.  17, 1910.  Device  for  Making 
Sub-surface  Tests  of  the  Bearing  Power  of  Soils  with  some  Examples  of 
Operation.  Eng.-Contr.,  v.  34,  p.  94,  Aug.  3,  1910.  Testing  Soil 
below  the  Surface  for  Foundation  Loads.  Eng.  Rec.,  v.  62,  p.  71,  July  16, 
1910;  v.  63,  p.  512,  May  6,  1911.  Testing  Foundations  at  the  Municipal 
Building,  New  York.  Eng.  Rec.,  v.  63,  p.  196,  Feb.  18,  1911.  Stand- 
ard Tests  of  Soil.  Rudolph  P.  Miller.  Eng.  Rec.,  v.  66,  p.  112,  July  27, 
1912.  Soil-Bearing  Tests.  Eng.  Rec.,  v.  66,  p.  304,  Sept.  14,  1912. 
Hard-Pan  and  Other  Soil  Tests.  J.  Norman  Jensen.  Eng.  News,  v.  69, 


ART.  206  EXPLORATIONS    AND    UNIT    LOADS  597 

p.  460,  Mar.  6,  1913;  see  also  editorial  on  p.  463.  Building  Foundations. 
J.  A.  Smith.  Jour.  Assoc.  Eng.  Soc.,  v.  36,  p.  155,  April,  1906.  Results 
of  Tests  on  Chicago  Hard-Pan  at  a  Depth  of  57  Feet  below  Lake  Level. 
Frank  A.  Randall.  Engr.-Contr.,  v.  37,  p.  436,  April  17,  1912. 

VALUES  OF  BEARING  CAPACITY. — Supporting  Power  of  Soils.  Randall 
Hunt.  Jour.  Assoc.  Eng.  Soc.,  v.  7,  p.  189,  June,  1888;  Eng.  News,  v.  19,  p. 
484,  June  16,  1888.  Construction  of  the  Buildings,  Bridges,  Piers,  and 
Docks  at  Jackson  Park.  Eng.  Rec.,  v.  28,  p.  199,  Aug.  26,  1893.  Al- 
lowable Pressure  on  Deep  Foundations.  Elmer  L.  Corthell.  Eng. 
News,  v.  56,  p.  657,  Dec.  20,  1906;  Editorial,  Eng.  Rec.,  v.  54,  p.  647, 
Dec.  15,  1906.  Foundation  Pressure  on  Hard-Pan;  Proposed  Rule. 
Rudolph  P.  Miller.  Eng.  News,  v.  64,  p.  727,  Dec.  29,  1910;  Eng.  Rec.,  v. 
62,  p.  783,  Dec.  31,  1910.  Sand  Foundations  for  High  Buildings. 
Eng.  Rec.,  v.  66,  p.  310,  Sept.  21,  1912.  Report  on  Unit  Pressure  Al- 
lowable on  Road-Beds  of  Different  Materials.  Proc.  Am.  Ry.  Eng.  Assoc., 
1912,  v.  13,  p.  388.  Failure  of  the  Transcona  Grain  Elevator.  Eng. 
News,  v.  70,  p.  944,  Nov.  6,  1913. 


INDEX 


ABBOTT,  H.,  139 
Abutments,  bridge,  433-451 

literature  of,  588 
buried,  449 

cubature  of  concrete,  445 
design  and  construction,  436 
form  and  dimensions,  433 
reinforced-arch,  449 
T-,  448 
U-,  441 
wing- wall,  439 

Air  chamber,  concreting,  322,  360,  552, 
see  also  pneumatic  caissons, 
working  chamber. 
Air-locks,  309,  352,  556 
American  Railway  Engineering  Asso- 
ciation, 6,  16,  55,  66, 112, 113 
Analysis  of  time  and  cost,  157 

BAINBRIDGE,  F.  H.,  449,  525 
Bearing,  allowable,  under  caissons,  559 
capacity,  tests  for,  531 

values  of,  534 
power,  effect  of  rest  on,  95 
sub-surface  conditions,  97 
taper,  166 
of  piles,  75-iiS 

literature  of,  572 
BERT,  P.,  332 
Blow-out  process,  319 
Borings  with  augers,  519 

wash,  520 

Box  caissons,  239-279 
literature  of,  580 
miscellaneous  types,  245 
of  concrete,  243 
of  timber,  240 
Breuchaud  process,  507 
Bridge  piers,  see  piers. 
BURNHAM  and  ROOT,  458 


Caisson  disease,  331,  333,  337 
Caissons,  box,  see  box  caissons. 

cylinder,  see  cylinder  caissons. 

definitions  and  classification,  239 

hydraulic,  382 

open,  see  open  caissons. 

pneumatic,  see  pneumatic  caissons. 
Caps,  pile,  27,  30,  147 
Chemical  preservation  of  piles,  63 
Chicago  method,  370 
Cofferdam  process,  198 
Cofferdams,  2,  198-238,  350 

choice  of  type,  238 

construction,  300 

cost  of,  236 

crib,  215,  226 

design  of,  235 

double- wall,  203,  213 

earth,  199 

leakage  of,  234 

literature  of,  577 

miscellaneous  types,  232 

movable,  228 
on  grillage,  231 

self-supporting,  221 

sheet-pile,  203,  206,  210,  216,  221 
steel,  216,  221 
supported  by  cribs,  214 
timber,  203 

single- wall,  206,  211 
Compressed  air,  physiological  effects, 

329 

Compressol  system,  181 
Concrete,  559 
Concrete  piles,  116-173 

advantages  of,  118 

cast-in-place,  116,  136 

choice  of  type,  163 

classification,  116 

cutting  off,  157 


599 


6oo 


INDEX 


Concrete  piles,  driving,  152 

effect  of  taper,  166 

form  and  construction,  130 

literature  of,  573 

precautions  against  injury,  142 

composite  types,  144 

pre- molded,  116 
design  of,  134 
patented,  127 
unpatented,  122 

specifications,  172 
COOPER,  T.,  391 
CORTHELL,  E.  L.,  535 
Cost  of  cofferdams,  236 

concrete  piles,  157 

pile  driving,  71,  157 
CRAWFORD,  J.  E.,  32 
Crib,  350 

construction,  298 
CUNNINGHAM,  A.  O.,  440 
Cutting  edge,  details  of,  294 
Cylinder  and  pivot  piers,  417-432 
Cylinder  caissons,  251,  304 

combination,  307 

literature  of,  581 

of  masonry,  252 

of  metal,  254 

of  reinforced  concrete,  257 

of  timber,  252 
Cylinders,  concreting  the,  513 

methods  of  sinking,  511 

pneumatic,  507 

transferring  load  to,  514 

Dam,  water-tight,  of  wall  piers,  361 
Design  of  bridge  abutments,  436 
Bridge  piers,  411 

caissons,  313 

cofferdams,  235 

cylinder  piers,  423 

double-column  footings,  464 

I-beam  grillages,  459,  464 

needle-beams,  492 

pneumatic  caissons,  313 

pre-molded  piles,  134 

reinforced-concrete  column   foot- 
ings, 477,  479 
spread  foundations,  474 


Design  of  sheet-piling,  194 
DOUGLAS,  W.  J.,  411 
Drilling,  core,  with  diamonds,  524 
without  diamonds,  527 

shot,  527 
Driving  batter  piles,  41 

concrete  piles,  152 

piles  butt  down,  40 

timber  piles,  37-74 
Drop-hammers,  20 

fall  of,  85 

restrained  fall,  87 

weights  of,  85,  148 

Engineering  literature,  564-597 
News  formula,  82,  91,  162 

Ejector,  hydraulic,  278 

Explorations,  518 
literature  of,  595 
sub-surface,  need  of,  529 

FAULKNER,  E.  O.,  n 

Followers,  27 

Footing,  design  of  reinforced-concrete 

column,  477,  479 
wall,  474 

distribution  of  pressure  on  base, 
468 

spread,  defined,  i 
Footings,  design  of  double-column,  464 

early  types,  453 

masonry,  453,  see  also  spread  foun- 
dations. 
Formulas  for  bearing  power  of  piles, 

77,  82,  90,  105,  161 
Foundation,  placing  the  new,  503 
Foundations,  i 

grillage,  see  spread  foundations. 

in  open  wells,  2 

open  caisson,  2 

pile,  defined,  2 

pneumatic,  2 

spread,  see  spread  foundations. 
Fox,  B.,  157 
Freezing  process,  379 
Frictional  resistance,  326 
FRIESTEDT,  L.  P.,  185    '\ 


INDEX 


601 


GIFFORD,  L.  R.,  189 
GOODRICH,  E.  P.,  13,  56,  77,  88 

formula,  77,  105 
GREINER,  J.  E.,  113, 172,  389, 391,  397, 

410,  436,  535 
Grouting  process,  373,  376,  378 

HARRIS,  R.  L.,  377 
Hydraulic  caissons,  382 

JACKSON,  J.  W.,  371 
JAMINET,  A.,  332 

KRIEGSMAN,  E.  F.,  94 

Leads,  pendulum,  42 

pile-driver,  14 
clearance  of,  10 

swinging,  42 

Lighting  of  pneumatic  caissons,  544 
Literature,  engineering,  564-597 
Loads,  unit,  518 

literature  of,  595 
Lock-joint  pipe,  70 
Low,  EMIL,  523 
LUTHER,  C.  M.,  449 

MCCLELLAN,  G.  B.,  48 

Mechanical  protection  of  piles,  66 
MERRILL,  O.,  517 
Metal  piles,  174-197 
MILLING WSKI,  A.  S.,  94 

MODJESKI,  R.,  402,  403 

MORAN,  D.  E.,  460 

MORSE,  E.  K.,  386 

MORISON,  G.  S.,  291,  294,  389,  395 

MURPHY,  M.,  420 

Needle-beams,  design  of,  492 
examples  with,  493 
supporting  wall  below,  495 

Needles,  figure-four,  501 

NEUKIRCH,  F.,  375 

NICHOLSON,  G.  B.,  87 

NOBLE,  A.,  403 

Overdriving  piles,  49 
Open  caissons,  2,  239-279 
literature  of,  580 


Open  caissons  of  concrete,  272 
of  metal,  270 
of  timber,  263 
single-wall,  246 
sinking,  277 
with  dredging  wells,  262 

Penetration  per  blow,  final,  88 

total,  100 

Pier  design,  example  of,  411 
\  foundations  in  open  wells,  366-383 

Piers,  bridge,  definitions,  386 

form  and  dimensions,  388 
general  requirements,  384 
literature  of,  588 
materials  and  construction,  394 
methods  of  failure,  411 
ordinary,  384-416 
specifications,  397 
cubature  of  concrete,  390 
cylinder,  417-432 

design  and  construction  of,  423 
metal  shell,  418 
on  piles,  418 
reinforced-concrete,  426 
hollow,  403 
pivot,  417-432 
solid,  examples  of,  398 
stability  of,  409,  424 
wall,  361 

Pile  caps,  27,  30,  147 
drivers,  14,  42,  147 

track,  i 6 

driving,  n,  37-55,  152,  169 
cost  of,  71 

diagrams  and  tables,  92 
literature  of,  567 
observations  in  practice,  37 
phenomena  of,  1 1 
hammer,  drop,  20,   147,  see  also 

drop-hammers. 

steam,  21,  147   see  also  steam- 
hammers, 
point,  32 

records  and  performance,  no 
rings,  27 
shoes,  32 
specifications,  112,  172 


602 


INDEX 


Pile  splices,  32 
Piles  acting  as  columns,  75 
batter,  3 

driving,  41 
bearing,  3,  4 
bearing  power  of,  75-115,  see  also 

bearing  power  of  piles, 
classification  of,  2 
combination,  5,  144 
concrete,  see  concrete  piles, 
cutting  off,  58,  157 
definitions  of,  2 
disk,  178 

driving  butt  down,  40 
guide,  4,  203,  206 
lagged,  8 
metal,  174-197 

literature  of,  575 
overdriving,  49 
pipe,  174 
reinforced-concrete,   see  concrete 

piles. 

removing,  58 
sand,  5,  180 
screw,  178 
sectional,  174 
sheet,  3,  i74-*97 
spacing  of,  55 
test,  n,  105,  169 
timber,  see  timber  piles, 
tubular,  174 

Piling,  sheet-,  see  sheet-piling. 
Plant  and  equipment,  555 
Pneumatic  caisson  practice,  538-561 
caissons,  bracing  of,  296 
building,  315 
caulking,  544 
cofferdam,  300,  350 
construction,  541 
crib,  298,  350 
cutting  edge,  294 
design  of,  313 
development,  338,  539 
excavation,  552 
for  bridges,  280-337 
literature  of,  582 
for  buildings,  338-365 
literature  of,  585 


Pneumatic  caissons,  friction  of,  326 
joints  between,  361,  554 
launching,  315,  547 
of  metal,  302,  345,  347 
of  reinforced-concrete,  301,  349 
of  timber,  340,  347 
placing,  315,  549 
removing  spoil,  319 
roof  construction,  283 
sealing,  322,  360,  552 
shafts  of,  309,  352,  544 
sinking,  317,  323,  356,  359,  549 
working    chamber,     293,    322 
360,  552 

Pneumatic  process,  280 

POETSCH,  F.  H.,  380 

PRIOR,  J.  H.,  451 

Puddle,  234 

Pump,  sand-and-mud,  321 

RAYMOND,  A.  A.,  116 
RIDGWAY,  ROBERT,  528 
ROBERTS,  T.  P.,  237 

SCHERMERHORN,  L.  Y.,  48 

SCHNEIDER,  C.  C.,  389,  534 

E.  J.,  432 

SEAMAN,  H.  B.,  534 
Security,  degree  of,  101 
Sheeting  in  open  wells,  370 
Sheet-piling,  3,  174-197 

concrete,  189 

design  of,  194 

driving,  190 

in  open  wells,  366 

steel,  184 

strength,  195 

supported  by  cribs,  214 
by  frames,  210 

timber,  181 

Wakefield,  182 
Sinking  open  caissons,  277 

pneumatic  caissons,  317,  323,  356, 
359,  549 

rate  of,  323,  359 
SMITH,  A.  H.,  332 

C.  S.,  67 
SNELL,  E.  H.,  336 


INDEX 


603 


SOOYSMITH,  W.,  321 

Sounding  rods,  518 

Specifications   for   bridge   abutments, 
436 

concrete  piles,  172 

timber  piles,  112 
Spread  foundations,  452-489 

concrete,  487 

design  of  reinforced-concrete,  474 

I-beam  grillages,  construction,  458 
design,  459 

literature  of,  592 

modern  types,  457 

steel   grillage,    469,  see  also  foot- 
ings. 

Stability  of  piers,  409,  424 
Steam-hammers,  21 

advantages  of,  24 

weights  of,  23,  148 

TALBOT,  A.  N.,  478 

Taper,  effect  of,  on  piles,  166 

Test  piles,  105,  169 

pits,  518 

Tests  for  bearing  capacity,  53 1 
THOMPSON,  S.  E.,  157 
THOMSON,  T.  K.,  296,  313,  336,  353, 

Si5,  538 
Timber  piles,  6,  567 

and  drivers,  1-36 

brooming  of,  29 

chemical  preservation,  63 

cutting  off,  58 

driving,  37-74 


Timber  piles,  durability  of,  8,  63 
form  and  dimensions,  9 
literature  of,  567 
mechanical  protection,  66 
specifications  for,  6,  7,  9,  112 
use  of,  5 

TORRANCE,  W.  M.,  441,  449,  451 

Underpinning  buildings,  490-517 

cantilever  method  of,  497 

literature  of,  593 

modern  methods,  515 

needle-beam,  490 

remarks  on,  560 
UPSON,  M.  M.,  162 
USINA,  D.  A.,  353,  362,  363 

WADDELL  and  HARRINGTON,  306 

Wales,  4 

Wall,  joining  to  the  old,  506 

footing,  474 
Water-jet,  147,  278 

equipment,  48 

literature  of,  570 

use  of  the,  43 
WELLINGTON,  A.  M.,  82,  84,  91,  105, 

no 
Wells,  open,  foundations  in,  366-383 

literature  of,  587 

with  sheeting,  370 

with  sheet-piling,  366 
WHITE,  L.,  528 
WHITTEMORE,  D.  J.,  28 


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